diff --git a/developer/src/kmc-convert/src/converter-messages.ts b/developer/src/kmc-convert/src/converter-messages.ts
index 3d5a614f15..10c559ccbf 100644
--- a/developer/src/kmc-convert/src/converter-messages.ts
+++ b/developer/src/kmc-convert/src/converter-messages.ts
@@ -58,6 +58,12 @@ export class ConverterMessages {
     `INFO: Input file ${def(o.inputFilename)} contains unsupported character '${def(o.output)}' at keyMap index ${def(o.keymapIndex)} on Keycode ${def(o.key)} (${def(o.KeyName)})`
   );
 
+  static ERROR_UndefinedActionDetected = SevError | 0x0009;
+  static Error_UndefinedActionDetected = (o: { inputFilename: string, action: string, KeyName: string, keymapIndex: string; }) => m(
+    this.ERROR_UndefinedActionDetected,
+    `${def(o.inputFilename)}: Action id ${def(o.action)} of key ${def(o.KeyName)} in keymapIndex ${def(o.keymapIndex)} is not defined`
+  );
+
   static ERROR_InvalidFile = SevError | 0x0008;
   static Error_InvalidFile = (o: { errorText: string; }) => m(
     this.ERROR_InvalidFile,
diff --git a/developer/src/kmc-convert/src/keylayout-to-kmn/keylayout-to-kmn-converter.ts b/developer/src/kmc-convert/src/keylayout-to-kmn/keylayout-to-kmn-converter.ts
index 9d995d0108..b52f81fb7f 100644
--- a/developer/src/kmc-convert/src/keylayout-to-kmn/keylayout-to-kmn-converter.ts
+++ b/developer/src/kmc-convert/src/keylayout-to-kmn/keylayout-to-kmn-converter.ts
@@ -337,6 +337,15 @@ export class KeylayoutToKmnConverter {
               // ...............................................................................................................................
 
               const b1ActionIndex: number = this.getActionIndexFromActionId(jsonObj, actionId);
+              if (b1ActionIndex < 0) {
+                this.callbacks.reportMessage(ConverterMessages.Error_UndefinedActionDetected({
+                  inputFilename: jsonObj.keyboard['@__name'] + ".keylayout",
+                  action: actionId,
+                  KeyName: this.mapUkeleleKeycodeToVK(jsonObj.keyboard.keyMapSet[0].keyMap[i].key[j]['@__code']),
+                  keymapIndex: jsonObj.keyboard.keyMapSet[0].keyMap[i]['@__index']
+                }));
+                return null;
+              }
 
               // with actionId from above loop all 'action' and search for a state(none)-next-pair ............................................................................................................
               // e.g. in Block 5: find <when state="none" next="1"/> for action id a18 ......................................................................................................................
@@ -807,7 +816,7 @@ export class KeylayoutToKmnConverter {
         return i;
       }
     }
-    return 0;
+    return -1;
   }
 
   /**
diff --git a/developer/src/kmc-convert/test/keylayout-to-kmn-converter.tests.ts b/developer/src/kmc-convert/test/keylayout-to-kmn-converter.tests.ts
index a1b7f7c750..c87be4708a 100644
--- a/developer/src/kmc-convert/test/keylayout-to-kmn-converter.tests.ts
+++ b/developer/src/kmc-convert/test/keylayout-to-kmn-converter.tests.ts
@@ -89,6 +89,19 @@ describe('KeylayoutToKmnConverter', function () {
     });
   });
 
+  describe('RunSpecialTestFiles - undefined action', function () {
+    const sut = new KeylayoutToKmnConverter(compilerTestCallbacks, compilerTestOptions);
+    [
+      [makePathToFixture('../data/Test_undefinedAction.keylayout')],
+    ].forEach(function (files) {
+      it(files + " should give Error: undefined action detected", async function () {
+        sut.run(files[0]);
+        assert.isTrue(compilerTestCallbacks.messages.length === 1);
+        assert.equal(compilerTestCallbacks.messages[0].code, 5292041);
+      });
+    });
+  });
+
   describe('run() ', function () {
     const sut = new KeylayoutToKmnConverter(compilerTestCallbacks, compilerTestOptions);
 
@@ -183,11 +196,11 @@ describe('KeylayoutToKmnConverter', function () {
     });
 
     it('should return empty on empty input', async function () {
-        assert.isNull(convertedEmpty)
+      assert.isNull(convertedEmpty);
     });
 
     it('should return empty on empty name as input', async function () {
-        assert.isNull(convertedUnavailable)
+      assert.isNull(convertedUnavailable);
     });
 
     it('should return empty on only modifiers as input', async function () {
@@ -196,7 +209,7 @@ describe('KeylayoutToKmnConverter', function () {
         modifiers: [['caps'], ['Shift'], ['command']],
         rules: []
       }, '');
-        assert.isNull(convertedMod)
+      assert.isNull(convertedMod);
     });
 
     it('should return empty on only rules as input', async function () {
@@ -205,12 +218,12 @@ describe('KeylayoutToKmnConverter', function () {
         modifiers: [],
         rules: [['C0', '', '', 0, 0, '', '', 0, 0, 'CAPS', 'K_A', 'A']]
       }, '');
-        assert.isNull(convertedRule)
+      assert.isNull(convertedRule);
     });
 
     it('should return empty array of rules on null input', async function () {
       const convertedRule = sut.convertBound.convert(null, 'ABC.kmn');
-        assert.isNull(convertedRule)
+      assert.isNull(convertedRule);
 
     });
   });
@@ -419,16 +432,16 @@ describe('KeylayoutToKmnConverter', function () {
     const read = sutR.read(inputFilename);
 
     [
-      ['none', 0],
+      ['none', -1],
       ['A_16', 8],
       ['A_18', 10],
       ['A_19', 11],
-      ['0', 0],
-      ['', 0],
-      [' ', 0],
-      [null, 0],
-      [undefined, 0],
-      ['unknown', 0],
+      ['0', -1],
+      ['', -1],
+      [' ', -1],
+      [null, -1],
+      [undefined, -1],
+      ['unknown', -1],
     ].forEach(function (values) {
       it(("getActionIndexFromActionId('" + values[0] + "')").padEnd(50, " ") + ' should return ' + values[1], async function () {
         const result = sut.getActionIndexFromActionId(read, String(values[0]));