diff --git a/javascript/ql/src/Security/CWE-020/IncompleteUrlSubstringSanitization.ql b/javascript/ql/src/Security/CWE-020/IncompleteUrlSubstringSanitization.ql
index 4c8b420583a..8394bbf1ee9 100644
--- a/javascript/ql/src/Security/CWE-020/IncompleteUrlSubstringSanitization.ql
+++ b/javascript/ql/src/Security/CWE-020/IncompleteUrlSubstringSanitization.ql
@@ -13,17 +13,27 @@
 import javascript
 private import semmle.javascript.dataflow.InferredTypes
 
-from DataFlow::MethodCallNode call, string name, DataFlow::Node substring, string target
+/**
+ * A check on a string for whether it contains a given substring, possibly with restrictions on the location of the substring.
+ */
+class SomeSubstringCheck extends DataFlow::Node {
+  DataFlow::Node substring;
+
+  SomeSubstringCheck() {
+    this.(StringOps::StartsWith).getSubstring() = substring or
+    this.(StringOps::Includes).getSubstring() = substring or
+    this.(StringOps::EndsWith).getSubstring() = substring
+  }
+
+  /**
+   * Gets the substring.
+   */
+  DataFlow::Node getSubstring() { result = substring }
+}
+
+from SomeSubstringCheck check, DataFlow::Node substring, string target, string msg
 where
-  (
-    name = "indexOf" or
-    name = "lastIndexOf" or
-    name = "includes" or
-    name = "startsWith" or
-    name = "endsWith"
-  ) and
-  call.getMethodName() = name and
-  substring = call.getArgument(0) and
+  substring = check.getSubstring() and
   substring.mayHaveStringValue(target) and
   (
     // target contains a domain on a common TLD, and perhaps some other URL components
@@ -34,33 +44,22 @@ where
     // target is a HTTP URL to a domain on any TLD
     target.regexpMatch("(?i)https?://([a-z0-9-]+\\.)+([a-z]+)(:[0-9]+)?/?")
   ) and
+  (
+    if check instanceof StringOps::StartsWith
+    then msg = "may be followed by an arbitrary host name"
+    else
+      if check instanceof StringOps::EndsWith
+      then msg = "may be preceded by an arbitrary host name"
+      else msg = "can be anywhere in the URL, and arbitrary hosts may come before or after it"
+  ) and
   // whitelist
   not (
-    (name = "indexOf" or name = "lastIndexOf") and
-    (
-      // arithmetic on the indexOf-result
-      any(ArithmeticExpr e).getAnOperand().getUnderlyingValue() = call.asExpr()
-      or
-      // non-trivial position check on the indexOf-result
-      exists(EqualityTest test, Expr n | test.hasOperands(call.asExpr(), n) |
-        not n.getIntValue() = [-1 .. 0]
-      )
-    )
-    or
     // the leading dot in a subdomain sequence makes the suffix-check safe (if it is performed on the host of the url)
-    name = "endsWith" and
+    check instanceof StringOps::EndsWith and
     target.regexpMatch("(?i)\\.([a-z0-9-]+)(\\.[a-z0-9-]+)+")
     or
     // the trailing port or slash makes the prefix-check safe
-    (
-      name = "startsWith"
-      or
-      name = "indexOf" and
-      exists(EqualityTest test, Expr n |
-        test.hasOperands(call.asExpr(), n) and
-        n.getIntValue() = 0
-      )
-    ) and
+    check instanceof StringOps::StartsWith and
     target.regexpMatch(".*(:[0-9]+|/)")
   )
-select call, "'$@' may be at an arbitrary position in the sanitized URL.", substring, target
+select check, "'$@' " + msg + ".", substring, target
diff --git a/javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSubstringSanitization.expected b/javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSubstringSanitization.expected
index 96e67f929c9..efbaad5a672 100644
--- a/javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSubstringSanitization.expected
+++ b/javascript/ql/test/query-tests/Security/CWE-020/IncompleteUrlSubstringSanitization.expected
@@ -1,18 +1,22 @@
-| tst-IncompleteUrlSubstringSanitization.js:4:5:4:27 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:4:15:4:26 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:5:5:5:27 | x.index ... e.net") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:5:15:5:26 | "secure.net" | secure.net |
-| tst-IncompleteUrlSubstringSanitization.js:6:5:6:28 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:6:15:6:27 | ".secure.com" | .secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:10:5:10:27 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:10:15:10:26 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:11:5:11:27 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:11:15:11:26 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:12:5:12:27 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:12:15:12:26 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:14:5:14:38 | x.start ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:14:18:14:37 | "https://secure.com" | https://secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:15:5:15:28 | x.endsW ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:15:16:15:27 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:20:5:20:28 | x.inclu ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:20:16:20:27 | "secure.com" | secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:32:5:32:35 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:32:15:32:34 | "https://secure.com" | https://secure.com |
-| tst-IncompleteUrlSubstringSanitization.js:33:5:33:39 | x.index ... m:443") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:33:15:33:38 | "https: ... om:443" | https://secure.com:443 |
-| tst-IncompleteUrlSubstringSanitization.js:34:5:34:36 | x.index ... .com/") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:34:15:34:35 | "https: ... e.com/" | https://secure.com/ |
-| tst-IncompleteUrlSubstringSanitization.js:52:5:52:41 | x.index ... ernal") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:52:15:52:40 | "https: ... ternal" | https://example.internal |
-| tst-IncompleteUrlSubstringSanitization.js:55:5:55:44 | x.start ... ernal") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:55:18:55:43 | "https: ... ternal" | https://example.internal |
-| tst-IncompleteUrlSubstringSanitization.js:56:5:56:45 | x.index ... l.org') | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:56:15:56:44 | 'https: ... al.org' | https://example.internal.org |
-| tst-IncompleteUrlSubstringSanitization.js:57:5:57:45 | x.index ... l.org') | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:57:15:57:44 | 'https: ... al.org' | https://example.internal.org |
-| tst-IncompleteUrlSubstringSanitization.js:58:5:58:30 | x.endsW ... l.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:58:16:58:29 | "internal.com" | internal.com |
-| tst-IncompleteUrlSubstringSanitization.js:61:2:61:24 | x.index ... e.com") | '$@' may be at an arbitrary position in the sanitized URL. | tst-IncompleteUrlSubstringSanitization.js:61:12:61:23 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:4:5:4:34 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:4:15:4:26 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:5:5:5:34 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:5:15:5:26 | "secure.net" | secure.net |
+| tst-IncompleteUrlSubstringSanitization.js:6:5:6:35 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:6:15:6:27 | ".secure.com" | .secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:10:5:10:34 | x.index ...  === -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:10:15:10:26 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:11:5:11:33 | x.index ... ) === 0 | '$@' may be followed by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:11:15:11:26 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:12:5:12:32 | x.index ... ") >= 0 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:12:15:12:26 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:14:5:14:38 | x.start ... e.com") | '$@' may be followed by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:14:18:14:37 | "https://secure.com" | https://secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:15:5:15:28 | x.endsW ... e.com") | '$@' may be preceded by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:15:16:15:27 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:20:5:20:28 | x.inclu ... e.com") | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:20:16:20:27 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:32:5:32:42 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:32:15:32:34 | "https://secure.com" | https://secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:33:5:33:46 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:33:15:33:38 | "https: ... om:443" | https://secure.com:443 |
+| tst-IncompleteUrlSubstringSanitization.js:34:5:34:43 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:34:15:34:35 | "https: ... e.com/" | https://secure.com/ |
+| tst-IncompleteUrlSubstringSanitization.js:52:5:52:48 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:52:15:52:40 | "https: ... ternal" | https://example.internal |
+| tst-IncompleteUrlSubstringSanitization.js:55:5:55:44 | x.start ... ernal") | '$@' may be followed by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:55:18:55:43 | "https: ... ternal" | https://example.internal |
+| tst-IncompleteUrlSubstringSanitization.js:56:5:56:51 | x.index ... ) !== 0 | '$@' may be followed by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:56:15:56:44 | 'https: ... al.org' | https://example.internal.org |
+| tst-IncompleteUrlSubstringSanitization.js:57:5:57:51 | x.index ... ) === 0 | '$@' may be followed by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:57:15:57:44 | 'https: ... al.org' | https://example.internal.org |
+| tst-IncompleteUrlSubstringSanitization.js:58:5:58:30 | x.endsW ... l.com") | '$@' may be preceded by an arbitrary host name. | tst-IncompleteUrlSubstringSanitization.js:58:16:58:29 | "internal.com" | internal.com |
+| tst-IncompleteUrlSubstringSanitization.js:61:2:61:31 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:61:12:61:23 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:62:2:62:31 | x.index ...  === -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:62:12:62:23 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:63:4:63:33 | x.index ...  !== -1 | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:63:14:63:25 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:64:3:64:26 | x.inclu ... e.com") | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:64:14:64:25 | "secure.com" | secure.com |
+| tst-IncompleteUrlSubstringSanitization.js:66:6:66:29 | x.inclu ... e.com") | '$@' can be anywhere in the URL, and arbitrary hosts may come before or after it. | tst-IncompleteUrlSubstringSanitization.js:66:17:66:28 | "secure.com" | secure.com |
diff --git a/javascript/ql/test/query-tests/Security/CWE-020/tst-IncompleteUrlSubstringSanitization.js b/javascript/ql/test/query-tests/Security/CWE-020/tst-IncompleteUrlSubstringSanitization.js
index de52d7c0e46..f7246c2a401 100644
--- a/javascript/ql/test/query-tests/Security/CWE-020/tst-IncompleteUrlSubstringSanitization.js
+++ b/javascript/ql/test/query-tests/Security/CWE-020/tst-IncompleteUrlSubstringSanitization.js
@@ -1,11 +1,11 @@
 (function(x){
-    x.indexOf("internal"); // NOT OK, but not flagged
-    x.indexOf("localhost"); // NOT OK, but not flagged
-    x.indexOf("secure.com"); // NOT OK
-    x.indexOf("secure.net"); // NOT OK
-    x.indexOf(".secure.com"); // NOT OK
-    x.indexOf("sub.secure."); // NOT OK, but not flagged
-    x.indexOf(".sub.secure."); // NOT OK, but not flagged
+    x.indexOf("internal") !== -1; // NOT OK, but not flagged
+    x.indexOf("localhost") !== -1; // NOT OK, but not flagged
+    x.indexOf("secure.com") !== -1; // NOT OK
+    x.indexOf("secure.net") !== -1; // NOT OK
+    x.indexOf(".secure.com") !== -1; // NOT OK
+    x.indexOf("sub.secure.") !== -1; // NOT OK, but not flagged
+    x.indexOf(".sub.secure.") !== -1; // NOT OK, but not flagged
 
     x.indexOf("secure.com") === -1; // NOT OK
     x.indexOf("secure.com") === 0; // NOT OK
@@ -19,38 +19,38 @@
 
     x.includes("secure.com"); // NOT OK
 
-    x.indexOf("#"); // OK
-    x.indexOf(":"); // OK
-    x.indexOf(":/"); // OK
-    x.indexOf("://"); // OK
-    x.indexOf("//"); // OK
-    x.indexOf(":443"); // OK
-    x.indexOf("/some/path/"); // OK
-    x.indexOf("some/path"); // OK
-    x.indexOf("/index.html"); // OK
-    x.indexOf(":template:"); // OK
-    x.indexOf("https://secure.com"); // NOT OK
-    x.indexOf("https://secure.com:443"); // NOT OK
-    x.indexOf("https://secure.com/"); // NOT OK
+    x.indexOf("#") !== -1; // OK
+    x.indexOf(":") !== -1; // OK
+    x.indexOf(":/") !== -1; // OK
+    x.indexOf("://") !== -1; // OK
+    x.indexOf("//") !== -1; // OK
+    x.indexOf(":443") !== -1; // OK
+    x.indexOf("/some/path/") !== -1; // OK
+    x.indexOf("some/path") !== -1; // OK
+    x.indexOf("/index.html") !== -1; // OK
+    x.indexOf(":template:") !== -1; // OK
+    x.indexOf("https://secure.com") !== -1; // NOT OK
+    x.indexOf("https://secure.com:443") !== -1; // NOT OK
+    x.indexOf("https://secure.com/") !== -1; // NOT OK
 
-    x.indexOf(".cn"); // NOT OK, but not flagged
-    x.indexOf(".jpg"); // OK
-    x.indexOf("index.html"); // OK
-    x.indexOf("index.js"); // OK
-    x.indexOf("index.php"); // OK
-    x.indexOf("index.css"); // OK
+    x.indexOf(".cn") !== -1; // NOT OK, but not flagged
+    x.indexOf(".jpg") !== -1; // OK
+    x.indexOf("index.html") !== -1; // OK
+    x.indexOf("index.js") !== -1; // OK
+    x.indexOf("index.php") !== -1; // OK
+    x.indexOf("index.css") !== -1; // OK
 
-    x.indexOf("secure=true"); // OK (query param)
-    x.indexOf("&auth="); // OK (query param)
+    x.indexOf("secure=true") !== -1; // OK (query param)
+    x.indexOf("&auth=") !== -1; // OK (query param)
 
-    x.indexOf(getCurrentDomain()); // NOT OK, but not flagged
-    x.indexOf(location.origin); // NOT OK, but not flagged
+    x.indexOf(getCurrentDomain()) !== -1; // NOT OK, but not flagged
+    x.indexOf(location.origin) !== -1; // NOT OK, but not flagged
 
-    x.indexOf("tar.gz") + offset // OK
-    x.indexOf("tar.gz") - offset // OK
+	x.indexOf("tar.gz") + offset; // OK
+	x.indexOf("tar.gz") - offset; // OK
 
-    x.indexOf("https://example.internal"); // NOT OK
-    x.indexOf("https://"); // OK
+    x.indexOf("https://example.internal") !== -1; // NOT OK
+    x.indexOf("https://") !== -1; // OK
 
     x.startsWith("https://example.internal"); // NOT OK
     x.indexOf('https://example.internal.org') !== 0; // NOT OK
@@ -59,4 +59,13 @@
     x.startsWith("https://example.internal:80"); // OK
 
 	x.indexOf("secure.com") !== -1; // NOT OK
+	x.indexOf("secure.com") === -1; // OK
+	!(x.indexOf("secure.com") !== -1); // OK
+	!x.includes("secure.com"); // OK
+
+	if(!x.includes("secure.com")) { // NOT OK
+
+	} else {
+		doSomeThingWithTrustedURL(x);
+	}
 });