diff --git a/python/ql/src/Security/CWE-020-ExternalAPIs/ExternalAPIs.qll b/python/ql/src/Security/CWE-020-ExternalAPIs/ExternalAPIs.qll
index 94494f3ca9b..ae2c9c273f5 100644
--- a/python/ql/src/Security/CWE-020-ExternalAPIs/ExternalAPIs.qll
+++ b/python/ql/src/Security/CWE-020-ExternalAPIs/ExternalAPIs.qll
@@ -43,7 +43,12 @@ private class DefaultSafeExternalApi extends SafeExternalApi {
   }
 }
 
-/** Gets a human readable representation of `node`. */
+/**
+ * Gets a human readable representation of `node`.
+ *
+ * Note that this is only defined for API nodes that are allowed as external APIs,
+ * so `None.json.dumps` will for example not be allowed.
+ */
 string apiNodeToStringRepr(API::Node node) {
   node = API::builtin(result)
   or
@@ -51,7 +56,8 @@ string apiNodeToStringRepr(API::Node node) {
   or
   exists(API::Node base, string basename |
     base.getDepth() < node.getDepth() and
-    basename = apiNodeToStringRepr(base)
+    basename = apiNodeToStringRepr(base) and
+    not base = API::builtin("None")
   |
     exists(string m | node = base.getMember(m) | result = basename + "." + m)
     or
diff --git a/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/ExternalAPIsUsedWithUntrustedData.expected b/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/ExternalAPIsUsedWithUntrustedData.expected
index 30220ea651d..a346aef9d22 100644
--- a/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/ExternalAPIsUsedWithUntrustedData.expected
+++ b/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/ExternalAPIsUsedWithUntrustedData.expected
@@ -1,5 +1,3 @@
-| None.json.dumps [position 0] | 1 | 1 |
-| builtins.None.json.dumps [position 0] | 1 | 1 |
 | hmac.new [keyword msg] | 1 | 1 |
 | hmac.new [position 1] | 1 | 1 |
 | unknown.lib.func [keyword kw] | 2 | 1 |
diff --git a/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/UntrustedDataToExternalAPI.expected b/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/UntrustedDataToExternalAPI.expected
index 708054a8dab..bb6ffaab366 100644
--- a/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/UntrustedDataToExternalAPI.expected
+++ b/python/ql/test/query-tests/Security/CWE-020-ExternalAPIs/UntrustedDataToExternalAPI.expected
@@ -51,5 +51,3 @@ subpaths
 | test.py:36:13:36:16 | ControlFlowNode for data | test.py:5:26:5:32 | ControlFlowNode for ImportMember | test.py:36:13:36:16 | ControlFlowNode for data | Call to unknown.lib.func [keyword kw] with untrusted data from $@. | test.py:5:26:5:32 | ControlFlowNode for ImportMember | ControlFlowNode for ImportMember |
 | test.py:43:22:43:25 | ControlFlowNode for data | test.py:5:26:5:32 | ControlFlowNode for ImportMember | test.py:43:22:43:25 | ControlFlowNode for data | Call to unknown.lib.func [position 0] with untrusted data from $@. | test.py:5:26:5:32 | ControlFlowNode for ImportMember | ControlFlowNode for ImportMember |
 | test.py:44:25:44:28 | ControlFlowNode for data | test.py:5:26:5:32 | ControlFlowNode for ImportMember | test.py:44:25:44:28 | ControlFlowNode for data | Call to unknown.lib.func [keyword kw] with untrusted data from $@. | test.py:5:26:5:32 | ControlFlowNode for ImportMember | ControlFlowNode for ImportMember |
-| test.py:50:32:50:34 | ControlFlowNode for arg | test.py:5:26:5:32 | ControlFlowNode for ImportMember | test.py:50:32:50:34 | ControlFlowNode for arg | Call to None.json.dumps [position 0] with untrusted data from $@. | test.py:5:26:5:32 | ControlFlowNode for ImportMember | ControlFlowNode for ImportMember |
-| test.py:50:32:50:34 | ControlFlowNode for arg | test.py:5:26:5:32 | ControlFlowNode for ImportMember | test.py:50:32:50:34 | ControlFlowNode for arg | Call to builtins.None.json.dumps [position 0] with untrusted data from $@. | test.py:5:26:5:32 | ControlFlowNode for ImportMember | ControlFlowNode for ImportMember |