diff --git a/ql/src/semmle/go/dataflow/Properties.qll b/ql/src/semmle/go/dataflow/Properties.qll
index c030f384a38..ac45742f4a0 100644
--- a/ql/src/semmle/go/dataflow/Properties.qll
+++ b/ql/src/semmle/go/dataflow/Properties.qll
@@ -14,12 +14,9 @@ private newtype TProperty =
  * Supported properties currently are Boolean truth and `nil`-ness.
  */
 class Property extends TProperty {
-  /**
-   * Holds if `test` evaluating to `outcome` means that this property holds of `nd`.
-   */
-  predicate checkOn(DataFlow::Node test, Boolean outcome, DataFlow::Node nd) {
+  private predicate checkOnExpr(Expr test, Boolean outcome, DataFlow::Node nd) {
     exists(EqualityTestExpr eq, Expr e, boolean isTrue |
-      eq = test.asExpr() and eq.hasOperands(nd.asExpr(), e)
+      eq = test and eq.hasOperands(nd.asExpr(), e)
     |
       this = IsBoolean(isTrue) and
       isTrue = eq.getPolarity().booleanXor(e.getBoolValue().booleanXor(outcome))
@@ -29,15 +26,44 @@ class Property extends TProperty {
       isTrue = eq.getPolarity().booleanXor(outcome).booleanNot()
     )
     or
-    test = nd and
-    test.asExpr() instanceof ValueExpr and
+    // if test = outcome ==> nd matches this
+    // then !test = !outcome ==> nd matches this
+    this.checkOnExpr(test.(NotExpr).getOperand(), outcome.booleanNot(), nd)
+    or
+    // if test = outcome ==> nd matches this
+    // then (test) = outcome ==> nd matches this
+    this.checkOnExpr(test.(ParenExpr).getExpr(), outcome, nd)
+    or
+    // if test = true ==> nd matches this
+    // then (test && e) = true ==> nd matches this
+    outcome = true and
+    this.checkOnExpr(test.(LandExpr).getAnOperand(), outcome, nd)
+    or
+    // if test = false ==> nd matches this
+    // then (test || e) = false ==> nd matches this
+    outcome = false and
+    this.checkOnExpr(test.(LorExpr).getAnOperand(), outcome, nd)
+    or
+    test = nd.asExpr() and
+    test instanceof ValueExpr and
     test.getType().getUnderlyingType() instanceof BoolType and
     this = IsBoolean(outcome)
   }
 
+  /**
+   * Holds if `test` evaluating to `outcome` means that this property holds of `nd`, where `nd` is a
+   * subexpression of `test`.
+   */
+  predicate checkOn(DataFlow::Node test, Boolean outcome, DataFlow::Node nd) {
+    checkOnExpr(test.asExpr(), outcome, nd)
+  }
+
   /** Holds if this is the property of having the Boolean value `b`. */
   predicate isBoolean(boolean b) { this = IsBoolean(b) }
 
+  /** Returns the boolean represented by this property if it is a boolean. */
+  boolean asBoolean() { this = IsBoolean(result) }
+
   /** Holds if this is the property of being `nil`. */
   predicate isNil() { this = IsNil(true) }
 
@@ -58,3 +84,18 @@ class Property extends TProperty {
     result = "is not nil"
   }
 }
+
+/**
+ * Gets a `Property` representing truth outcome `b`.
+ */
+Property booleanProperty(boolean b) { result = IsBoolean(b) }
+
+/**
+ * Gets a `Property` representing `nil`-ness.
+ */
+Property nilProperty() { result = IsNil(true) }
+
+/**
+ * Gets a `Property` representing non-`nil`-ness.
+ */
+Property notNilProperty() { result = IsNil(false) }
diff --git a/ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll b/ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll
index 780db1d9ab0..d2bd8246b3f 100644
--- a/ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll
+++ b/ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll
@@ -1143,28 +1143,65 @@ abstract class BarrierGuard extends Node {
    * We check this by looking for guards on `inp` that dominate a `return` statement that
    * is the only `return` in `f` that can return `true`. This means that if `f` returns `true`,
    * the guard must have been satisfied. (Similar reasoning is applied for statements returning
-   * `false` or a non-`nil` value.)
+   * `false`, `nil` or a non-`nil` value.)
    */
   private predicate guardingFunction(
     Function f, FunctionInput inp, FunctionOutput outp, DataFlow::Property p
   ) {
-    exists(ControlFlow::ConditionGuardNode guard, Node arg, FuncDecl fd, Node ret |
+    exists(FuncDecl fd, Node arg, Node ret |
       fd.getFunction() = f and
-      guards(guard, arg) and
       localFlow(inp.getExitNode(fd), arg) and
       ret = outp.getEntryNode(fd) and
-      guard.dominates(ret.getBasicBlock())
-    |
-      exists(boolean b |
-        onlyPossibleReturnOfBool(fd, outp, ret, b) and
-        p.isBoolean(b)
+      // Case: a function like "if someBarrierGuard(arg) { return true } else { return false }"
+      (
+        exists(ControlFlow::ConditionGuardNode guard |
+          guards(guard, arg) and
+          guard.dominates(ret.getBasicBlock())
+        |
+          exists(boolean b |
+            onlyPossibleReturnOfBool(fd, outp, ret, b) and
+            p.isBoolean(b)
+          )
+          or
+          onlyPossibleReturnOfNonNil(fd, outp, ret) and
+          p.isNonNil()
+          or
+          onlyPossibleReturnOfNil(fd, outp, ret) and
+          p.isNil()
+        )
+        or
+        // Case: a function like "return someBarrierGuard(arg)"
+        // or "return !someBarrierGuard(arg) && otherCond(...)"
+        exists(boolean outcome |
+          not exists(DataFlow::Node otherRet | otherRet = outp.getEntryNode(fd) | otherRet != ret) and
+          this.checks(arg.asExpr(), outcome) and
+          // This predicate's contract is (p holds of ret ==> arg is checked),
+          // (and we have (this has outcome ==> arg is checked))
+          // but p.checkOn(ret, outcome, this) gives us (ret has outcome ==> p holds of this),
+          // so we need to swap outcome and (specifically boolean) p:
+          DataFlow::booleanProperty(outcome).checkOn(ret, p.asBoolean(), this)
+        )
+        or
+        // Case: a function like "return guardProxy(arg)"
+        // or "return !guardProxy(arg) || otherCond(...)"
+        exists(
+          Function f2, FunctionInput inp2, FunctionOutput outp2, CallNode c,
+          DataFlow::Property outpProp
+        |
+          not exists(DataFlow::Node otherRet | otherRet = outp.getEntryNode(fd) | otherRet != ret) and
+          guardingFunction(f2, inp2, outp2, outpProp) and
+          c = f2.getACall() and
+          arg = inp2.getNode(c) and
+          (
+            // See comment above ("This method's contract...") for rationale re: the inversion of
+            // `p` and `outpProp` here:
+            outpProp.checkOn(ret, p.asBoolean(), outp2.getNode(c))
+            or
+            // The particular case where p is non-boolean (i.e., nil or non-nil), and we directly return `c`:
+            outpProp = p and ret = outp2.getNode(c)
+          )
+        )
       )
-      or
-      onlyPossibleReturnOfNonNil(fd, outp, ret) and
-      p.isNonNil()
-      or
-      onlyPossibleReturnOfNil(fd, outp, ret) and
-      p.isNil()
     )
   }
 }
@@ -1212,7 +1249,7 @@ private predicate onlyPossibleReturnOfNonNil(FuncDecl fd, FunctionOutput res, No
 }
 
 /**
- * Holds if function `f`'s result `output`, which must be a return value, is always non-nil.
+ * Holds if function `f`'s result `output`, which must be a return value, cannot be nil.
  */
 private predicate certainlyReturnsNonNil(Function f, FunctionOutput output) {
   output.isResult(_) and
@@ -1228,7 +1265,7 @@ private predicate certainlyReturnsNonNil(Function f, FunctionOutput output) {
 }
 
 /**
- * Holds if `node` is always non-nil.
+ * Holds if `node` cannot be `nil`.
  */
 private predicate isCertainlyNotNil(DataFlow::Node node) {
   node instanceof DataFlow::AddressOperationNode
diff --git a/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.expected b/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.expected
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.go b/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.go
new file mode 100644
index 00000000000..729c9518e55
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.go
@@ -0,0 +1,828 @@
+package main
+
+import (
+	"errors"
+)
+
+// Utilities: a source, a sink and a barrier guard ("isBad"):
+
+func source() string {
+	return "tainted"
+}
+
+func sink(s string) {}
+
+func isBad(s string) bool {
+	return len(s)%2 == 0
+}
+
+// Candidate barrier guard functions:
+
+// Validates when returning nil
+func guard(p string) error {
+	if isBad(p) {
+		return errors.New("zip contents corrupted")
+	}
+	return nil
+}
+
+// Validates when returning false
+func guardBool(p string) bool {
+	return isBad(p)
+}
+
+// Validates when returning false
+func guardBoolStmt(p string) bool {
+	if isBad(p) {
+		return true
+	}
+	return false
+}
+
+// Validates arg2 when returning true
+func juggleParams(arg1, arg2 string) bool {
+	return arg1 == "hello world" && !guardBool(arg2)
+}
+
+// Valid when returning true
+func guardBoolNeg(p string) bool {
+	return !isBad(p)
+}
+
+// Valid when returning false
+func guardBoolCmp(p string) bool {
+	return isBad(p) == true
+}
+
+// Valid when returning true
+func guardBoolNegCmp(p string) bool {
+	return isBad(p) != true
+}
+
+// Valid when returning false
+func guardBoolLOrLhs(p string) bool {
+	return isBad(p) || p == "hello world"
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegLhs(p string) bool {
+	return !isBad(p) || p == "hello world"
+}
+
+// Valid when returning false
+func guardBoolLOrRhs(p string) bool {
+	return p == "hello world" || isBad(p)
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegRhs(p string) bool {
+	return p == "hello world" || !isBad(p)
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndLhs(p string) bool {
+	return isBad(p) && p != "hello world"
+}
+
+// Valid when returning true
+func guardBoolLAndNegLhs(p string) bool {
+	return !isBad(p) && p != "hello world"
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndRhs(p string) bool {
+	return p != "hello world" && isBad(p)
+}
+
+// Valid when returning true
+func guardBoolLAndNegRhs(p string) bool {
+	return p != "hello world" && !isBad(p)
+}
+
+// Valid when returning false
+func guardBoolProxy(p string) bool {
+	return guardBool(p)
+}
+
+// Valid when returning true
+func guardBoolNegProxy(p string) bool {
+	return !guardBool(p)
+}
+
+// Valid when returning false
+func guardBoolCmpProxy(p string) bool {
+	return guardBool(p) == true
+}
+
+// Valid when returning true
+func guardBoolNegCmpProxy(p string) bool {
+	return guardBool(p) != true
+}
+
+// Valid when returning false
+func guardBoolLOrLhsProxy(p string) bool {
+	return guardBool(p) || p == "hello world"
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegLhsProxy(p string) bool {
+	return !guardBool(p) || p == "hello world"
+}
+
+// Valid when returning false
+func guardBoolLOrRhsProxy(p string) bool {
+	return p == "hello world" || guardBool(p)
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegRhsProxy(p string) bool {
+	return p == "hello world" || !guardBool(p)
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndLhsProxy(p string) bool {
+	return guardBool(p) && p != "hello world"
+}
+
+// Valid when returning true
+func guardBoolLAndNegLhsProxy(p string) bool {
+	return !guardBool(p) && p != "hello world"
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndRhsProxy(p string) bool {
+	return p != "hello world" && guardBool(p)
+}
+
+// Valid when returning true
+func guardBoolLAndNegRhsProxy(p string) bool {
+	return p != "hello world" && !guardBool(p)
+}
+
+// Valid when returning true
+func guardProxyNilToBool(p string) bool {
+	return guard(p) == nil
+}
+
+// Valid when returning false
+func guardNeqProxyNilToBool(p string) bool {
+	return guard(p) != nil
+}
+
+// Valid when returning false
+func guardNotEqProxyNilToBool(p string) bool {
+	return !(guard(p) == nil)
+}
+
+// Valid when returning false
+func guardLOrLhsProxyNilToBool(p string) bool {
+	return guard(p) != nil || p == "hello world"
+}
+
+// Doesn't reliably validate p
+func guardLOrNegLhsProxyNilToBool(p string) bool {
+	return guard(p) == nil || p == "hello world"
+}
+
+// Valid when returning false
+func guardLOrRhsProxyNilToBool(p string) bool {
+	return p == "hello world" || guard(p) != nil
+}
+
+// Doesn't reliably validate p
+func guardLOrNegRhsProxyNilToBool(p string) bool {
+	return p == "hello world" || guard(p) == nil
+}
+
+// Doesn't reliably validate p
+func guardLAndLhsProxyNilToBool(p string) bool {
+	return guard(p) != nil && p != "hello world"
+}
+
+// Valid when returning true
+func guardLAndNegLhsProxyNilToBool(p string) bool {
+	return guard(p) == nil && p != "hello world"
+}
+
+// Doesn't reliably validate p
+func guardLAndRhsProxyNilToBool(p string) bool {
+	return p != "hello world" && !(guard(p) == nil)
+}
+
+// Valid when returning true
+func guardLAndNegRhsProxyNilToBool(p string) bool {
+	return p != "hello world" && guard(p) == nil
+}
+
+type retStruct struct {
+	s string
+}
+
+// Valid when returning nil
+func guardBoolProxyToNil(p string) *retStruct {
+	if guardBool(p) {
+		return &retStruct{"bad"}
+	}
+	return nil
+}
+
+// Valid when returning non-nil
+func guardBoolNegProxyToNil(p string) *retStruct {
+	if !guardBool(p) {
+		return &retStruct{"good"}
+	}
+	return nil
+}
+
+// Valid when returning nil
+func guardBoolCmpProxyToNil(p string) *retStruct {
+	if guardBool(p) == true {
+		return &retStruct{"bad"}
+	}
+	return nil
+}
+
+// Valid when returning non-nil
+func guardBoolNegCmpProxyToNil(p string) *retStruct {
+	if guardBool(p) != true {
+		return &retStruct{"good"}
+	}
+	return nil
+}
+
+// Valid when returning nil
+func guardBoolLOrLhsProxyToNil(p string) *retStruct {
+	if guardBool(p) || p == "hello world" {
+		return &retStruct{"bad"}
+	}
+	return nil
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegLhsProxyToNil(p string) *retStruct {
+	if !guardBool(p) || p == "hello world" {
+		return &retStruct{"inconclusive"}
+	}
+	return nil
+}
+
+// Valid when returning nil
+func guardBoolLOrRhsProxyToNil(p string) *retStruct {
+	if p == "hello world" || guardBool(p) {
+		return &retStruct{"bad"}
+	}
+	return nil
+}
+
+// Doesn't reliably validate p
+func guardBoolLOrNegRhsProxyToNil(p string) *retStruct {
+	if p == "hello world" || !guardBool(p) {
+		return &retStruct{"inconclusive"}
+	}
+	return nil
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndLhsProxyToNil(p string) *retStruct {
+	if guardBool(p) && p != "hello world" {
+		return &retStruct{"inconclusive"}
+	}
+	return nil
+}
+
+// Valid when returning non-nil
+func guardBoolLAndNegLhsProxyToNil(p string) *retStruct {
+	if !guardBool(p) && p != "hello world" {
+		return &retStruct{"good"}
+	}
+	return nil
+}
+
+// Doesn't reliably validate p
+func guardBoolLAndRhsProxyToNil(p string) *retStruct {
+	if p != "hello world" && guardBool(p) {
+		return &retStruct{"inconclusive"}
+	}
+	return nil
+}
+
+// Valid when returning non-nil
+func guardBoolLAndNegRhsProxyToNil(p string) *retStruct {
+	if p != "hello world" && !guardBool(p) {
+		return &retStruct{"good"}
+	}
+	return nil
+}
+
+// Valid when returning nil
+func directProxyNil(p string) error {
+	return guard(p)
+}
+
+// Valid when returning true
+func deeplyNestedConditionalLeft(p string) bool {
+	return !isBad(p) && len(p)%2 == 1 && p[0] == 'a' && p[1] == 'b'
+}
+
+// Valid when returning true
+func deeplyNestedConditionalMiddle(p string) bool {
+	return len(p)%2 == 1 && p[0] == 'a' && !isBad(p) && p[1] == 'b'
+}
+
+// Valid when returning true
+func deeplyNestedConditionalRight(p string) bool {
+	return p[1] == 'b' && len(p)%2 == 1 && p[0] == 'a' && !isBad(p)
+}
+
+// Finally, actually test the functions -- try sinking a tainted value in the is-true/false
+// or is-nil/non-nil case for each candidate:
+
+func test() {
+
+	{
+		s := source()
+		if guardBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolStmt(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if juggleParams("other arg", s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNeg(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolCmp(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNegCmp(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrLhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegLhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrRhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegRhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndLhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegLhs(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndRhs(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegRhs(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNegProxy(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolCmpProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNegCmpProxy(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrLhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegLhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrRhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegRhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndLhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegLhsProxy(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndRhsProxy(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegRhsProxy(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardProxyNilToBool(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardNeqProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardNotEqProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardLOrLhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardLOrNegLhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardLOrRhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardLOrNegRhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardLAndLhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardLAndNegLhsProxyNilToBool(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardLAndRhsProxyNilToBool(s) {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardLAndNegRhsProxyNilToBool(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guard(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolProxyToNil(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNegProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolCmpProxyToNil(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolNegCmpProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrLhsProxyToNil(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegLhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrRhsProxyToNil(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLOrNegRhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndLhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegLhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndRhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if guardBoolLAndNegRhsProxyToNil(s) == nil {
+			sink(s) // $dataflow=s
+		} else {
+			sink(s)
+		}
+	}
+
+	{
+		s := source()
+		if directProxyNil(s) == nil {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if deeplyNestedConditionalLeft(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if deeplyNestedConditionalMiddle(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+	{
+		s := source()
+		if deeplyNestedConditionalRight(s) {
+			sink(s)
+		} else {
+			sink(s) // $dataflow=s
+		}
+	}
+
+}
diff --git a/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.ql b/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.ql
new file mode 100644
index 00000000000..a4d92e1fc7a
--- /dev/null
+++ b/ql/test/library-tests/semmle/go/dataflow/GuardingFunctions/test.ql
@@ -0,0 +1,39 @@
+import go
+import TestUtilities.InlineExpectationsTest
+
+class IsBad extends DataFlow::BarrierGuard, DataFlow::CallNode {
+  IsBad() { this.getTarget().getName() = "isBad" }
+
+  override predicate checks(Expr e, boolean branch) {
+    e = this.getAnArgument().asExpr() and branch = false
+  }
+}
+
+class TestConfig extends DataFlow::Configuration {
+  TestConfig() { this = "test config" }
+
+  override predicate isSource(DataFlow::Node source) {
+    source.(DataFlow::CallNode).getTarget().getName() = "source"
+  }
+
+  override predicate isSink(DataFlow::Node sink) {
+    sink = any(DataFlow::CallNode c | c.getTarget().getName() = "sink").getAnArgument()
+  }
+
+  override predicate isBarrierGuard(DataFlow::BarrierGuard bg) { bg instanceof IsBad }
+}
+
+class DataFlowTest extends InlineExpectationsTest {
+  DataFlowTest() { this = "DataFlowTest" }
+
+  override string getARelevantTag() { result = "dataflow" }
+
+  override predicate hasActualResult(string file, int line, string element, string tag, string value) {
+    tag = "dataflow" and
+    exists(DataFlow::Node sink | any(TestConfig c).hasFlow(_, sink) |
+      element = sink.toString() and
+      value = sink.toString() and
+      sink.hasLocationInfo(file, line, _, _, _)
+    )
+  }
+}