diff --git a/python/ql/lib/semmle/python/ApiGraphs.qll b/python/ql/lib/semmle/python/ApiGraphs.qll
index 77574ab44ad..e8fc14d90fd 100644
--- a/python/ql/lib/semmle/python/ApiGraphs.qll
+++ b/python/ql/lib/semmle/python/ApiGraphs.qll
@@ -349,8 +349,8 @@ module API {
       result.getAnImmediateUse() = this
     }
 
-    /** Gets the number of arguments of this call. */
-    int getNumArgument() { result = count(this.getArg(_)) }
+    /** Gets the number of arguments of this call. Both positional and named arguments are counted. */
+    int getNumArgument() { result = count([this.getArg(_), this.getArgByName(_)]) }
   }
 
   /**
diff --git a/python/ql/test/library-tests/frameworks/data/test.expected b/python/ql/test/library-tests/frameworks/data/test.expected
index 721854dad37..8fb6efc0f95 100644
--- a/python/ql/test/library-tests/frameworks/data/test.expected
+++ b/python/ql/test/library-tests/frameworks/data/test.expected
@@ -46,6 +46,8 @@ isSink
 | test.py:85:8:85:53 | ControlFlowNode for Attribute() | test-sink |
 | test.py:86:8:86:60 | ControlFlowNode for Attribute() | test-sink |
 | test.py:87:8:87:67 | ControlFlowNode for Attribute() | test-sink |
+| test.py:89:21:89:23 | ControlFlowNode for one | test-source |
+| test.py:90:25:90:27 | ControlFlowNode for one | test-source |
 isSource
 | test.py:3:5:3:15 | ControlFlowNode for getSource() | test-source |
 | test.py:9:8:9:14 | ControlFlowNode for alias() | test-source |
diff --git a/python/ql/test/library-tests/frameworks/data/test.py b/python/ql/test/library-tests/frameworks/data/test.py
index db8e8c98e91..96f09c51598 100644
--- a/python/ql/test/library-tests/frameworks/data/test.py
+++ b/python/ql/test/library-tests/frameworks/data/test.py
@@ -84,4 +84,9 @@ mySink(Steps.preserveArgZeroAndTwo("foo", "bar", getSource())) # FLOW
 
 mySink(Steps.preserveAllButFirstArgument(getSource())) # NO FLOW
 mySink(Steps.preserveAllButFirstArgument("foo", getSource())) # FLOW
-mySink(Steps.preserveAllButFirstArgument("foo", "bar", getSource())) # FLOW
\ No newline at end of file
+mySink(Steps.preserveAllButFirstArgument("foo", "bar", getSource())) # FLOW
+
+CallFilter.arityOne(one) # match
+CallFilter.arityOne(one=one) # match
+CallFilter.arityOne(one, two=two) # NO match
+CallFilter.arityOne(one=one, two=two) # NO match
diff --git a/python/ql/test/library-tests/frameworks/data/test.ql b/python/ql/test/library-tests/frameworks/data/test.ql
index d694837b253..2558631cec6 100644
--- a/python/ql/test/library-tests/frameworks/data/test.ql
+++ b/python/ql/test/library-tests/frameworks/data/test.ql
@@ -41,7 +41,7 @@ class Sinks extends ModelInput::SinkModelCsv {
         "testlib;;Member[Args].Member[lastarg].Argument[N-1];test-source", //
         "testlib;;Member[Args].Member[nonFist].Argument[1..];test-source", //
         // callsite filter.
-        "testlib;;Member[CallFilter].Member[arityOne].WithArity[1].Argument[0..];test-source", //
+        "testlib;;Member[CallFilter].Member[arityOne].WithArity[1].Argument[any];test-source", //
         "testlib;;Member[CallFilter].Member[twoOrMore].WithArity[2..].Argument[0..];test-source", //
         // testing non-positional arguments
         "testlib;;Member[ArgPos].Member[selfThing].Argument[self];test-source", //