diff --git a/developer/src/kmc-kmn/src/compiler/compiler.ts b/developer/src/kmc-kmn/src/compiler/compiler.ts
index df20b69852..317cfc757c 100644
--- a/developer/src/kmc-kmn/src/compiler/compiler.ts
+++ b/developer/src/kmc-kmn/src/compiler/compiler.ts
@@ -298,6 +298,12 @@ export class KmnCompiler implements UnicodeSetParser {
 
       if(wasm_result.extra.targets & COMPILETARGETS_JS) {
         wasm_options.target = 1; // CKF_KEYMANWEB TODO use COMPILETARGETS_JS
+
+        // We always want debug data in the intermediate .kmx, so that error
+        // messages from KMW compiler can give line numbers in .kmn. This
+        // should have no impact on the final .js if options.debug is false
+        wasm_options.saveDebug = true;
+
         wasm_result = Module.kmcmp_compile(infile, wasm_options, wasm_interface);
         if(!wasm_result.result) {
           return null;
diff --git a/developer/src/kmc-kmn/src/kmw-compiler/javascript-strings.ts b/developer/src/kmc-kmn/src/kmw-compiler/javascript-strings.ts
index bafbae2794..b7b9817572 100644
--- a/developer/src/kmc-kmn/src/kmw-compiler/javascript-strings.ts
+++ b/developer/src/kmc-kmn/src/kmw-compiler/javascript-strings.ts
@@ -490,7 +490,7 @@ function JavaScript_CompositeContextValue(fk: KMX.KEYBOARD, fkp: KMX.KEY, pwsz:
           `this.s${JavaScript_Name(rec.Any.StoreIndex, rec.Any.Store.dpName)})`;
         break;
       default:
-        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({code: GetCodeName(rec.Code)}));
+        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({line: fkp.Line, code: GetCodeName(rec.Code)}));
         Result += '/*.*/ 0 ';
       }
     }
@@ -579,7 +579,7 @@ function JavaScript_FullContextValue(fk: KMX.KEYBOARD, fkp: KMX.KEY, pwsz: strin
           `o:${rec.Index.Index}}`;   // I4611
         break;
       default:
-        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({code: GetCodeName(rec.Code)}));
+        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({line: fkp.Line, code: GetCodeName(rec.Code)}));
         Result += '/*.*/ 0 ';
       }
     }
@@ -677,7 +677,7 @@ export function JavaScript_OutputString(fk: KMX.KEYBOARD, FTabStops: string, fkp
           // These have no output for a context emit
           break;
       default:
-        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({code: GetCodeName(recContext.Code)}));
+        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebContext({line: fkp.Line, code: GetCodeName(recContext.Code)}));
         Result += nlt + '/*.*/ ';   // I4611
       }
     }
@@ -885,7 +885,7 @@ export function JavaScript_OutputString(fk: KMX.KEYBOARD, FTabStops: string, fkp
         len = -1;
         break;
       default:
-        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebOutput({code: GetCodeName(rec.Code)}));
+        callbacks.reportMessage(KmwCompilerMessages.Error_NotSupportedInKeymanWebOutput({line: fkp.Line, code: GetCodeName(rec.Code)}));
         Result += '';
       }
     }
diff --git a/developer/src/kmc-kmn/src/kmw-compiler/kmw-compiler-messages.ts b/developer/src/kmc-kmn/src/kmw-compiler/kmw-compiler-messages.ts
index 0c2e5bbdb6..a952125571 100644
--- a/developer/src/kmc-kmn/src/kmw-compiler/kmw-compiler-messages.ts
+++ b/developer/src/kmc-kmn/src/kmw-compiler/kmw-compiler-messages.ts
@@ -1,5 +1,6 @@
 import { KmnCompilerMessages } from "../compiler/kmn-compiler-messages.js";
-import { CompilerErrorNamespace, CompilerErrorSeverity, CompilerMessageSpec as m } from "@keymanapp/common-types";
+import { CompilerErrorNamespace, CompilerErrorSeverity, CompilerEvent, CompilerMessageSpec } from "@keymanapp/common-types";
+import { kmnfile } from "./compiler-globals.js";
 
 const Namespace = CompilerErrorNamespace.KmwCompiler;
 // const SevInfo = CompilerErrorSeverity.Info | Namespace;
@@ -8,6 +9,12 @@ const Namespace = CompilerErrorNamespace.KmwCompiler;
 const SevError = CompilerErrorSeverity.Error | Namespace;
 // const SevFatal = CompilerErrorSeverity.Fatal | Namespace;
 
+const m = (code: number, message: string, o?: {e?: any, filename?: string, line?: number}) : CompilerEvent => ({
+  ...CompilerMessageSpec(code, message, o?.e),
+  filename: o?.filename ?? kmnfile,
+  line: o?.line,
+});
+
 export class KmwCompilerMessages extends KmnCompilerMessages {
   // Note: for legacy reasons, KMWCompilerMessages extends from
   // KMNCompilerMessages as they share the same error codes. This can be a
@@ -19,44 +26,66 @@ export class KmwCompilerMessages extends KmnCompilerMessages {
 
   static Error_InvalidBegin = () => m(this.ERROR_InvalidBegin,
     `A "begin unicode" statement is required to compile a KeymanWeb keyboard`);
+
   static Error_InvalidTouchLayoutFile = (o:{filename:string}) => m(this.ERROR_InvalidTouchLayoutFile,
     `Touch layout file ${o.filename} is not valid`);
+
   static Warn_DontMixChiralAndNonChiralModifiers = () => m(this.WARN_DontMixChiralAndNonChiralModifiers,
     `This keyboard contains Ctrl,Alt and LCtrl,LAlt,RCtrl,RAlt sets of modifiers. Use only one or the other set for web target.`);
+
   static Warn_OptionStoreNameInvalid = (o:{name:string}) => m(this.WARN_OptionStoreNameInvalid,
     `The option store ${o.name} should be named with characters in the range A-Z, a-z, 0-9 and _ only.`);
+
   static Error_VirtualCharacterKeysNotSupportedInKeymanWeb = () => m(this.ERROR_VirtualCharacterKeysNotSupportedInKeymanWeb,
     `Virtual character keys not currently supported in KeymanWeb`);
+
   static Error_VirtualKeysNotValidForMnemonicLayouts = () => m(this.ERROR_VirtualKeysNotValidForMnemonicLayouts,
     `Virtual keys are not valid for mnemonic layouts`);
+
   static Warn_ExtendedShiftFlagsNotSupportedInKeymanWeb = (o:{flags:string}) => m(this.WARN_ExtendedShiftFlagsNotSupportedInKeymanWeb,
     `Extended shift flags ${o.flags} are not supported in KeymanWeb`);
+
   static Hint_UnreachableKeyCode = (o:{key:string}) => m(this.HINT_UnreachableKeyCode,
     `The rule will never be matched for key ${o.key} because its key code is never fired.`);
+
   static Error_NotSupportedInKeymanWebStore = (o:{code:string,store:string}) => m(this.ERROR_NotSupportedInKeymanWebStore,
-    `${o.code} is not currently supported in store '${o.store}' when used by any or index`);
-  static Error_NotSupportedInKeymanWebContext = (o:{code:String}) => m(this.ERROR_NotSupportedInKeymanWebContext,
-    `Statement ${o.code} is not currently supported in context`);
-  static Error_NotSupportedInKeymanWebOutput = (o:{code:string}) => m(this.ERROR_NotSupportedInKeymanWebOutput,
-    `Statement ${o.code} is not currently supported in output`);
+    `'${o.code}' is not currently supported in store '${o.store}' when used by any or index for web and touch targets`);
+
+  static Error_NotSupportedInKeymanWebContext = (o:{line:number, code:String}) => m(this.ERROR_NotSupportedInKeymanWebContext,
+    `Statement '${o.code}' is not currently supported in context for web and touch targets`, o);
+
+  static Error_NotSupportedInKeymanWebOutput = (o:{line:number, code:string}) => m(this.ERROR_NotSupportedInKeymanWebOutput,
+    `Statement '${o.code}' is not currently supported in output for web and touch targets`, o);
+
   static Warn_HelpFileMissing = (o:{filename: string, e:any}) => m(this.WARN_HelpFileMissing,
     `File ${o.filename} could not be loaded: ${(o.e??'').toString()}`);
+
   static Warn_EmbedJsFileMissing = (o:{filename: string, e:any}) => m(this.WARN_EmbedJsFileMissing,
     `File ${o.filename} could not be loaded: ${(o.e??'').toString()}`);
+
   static Warn_TouchLayoutMissingLayer = (o:{keyId:string, platformName:string, layerId:string, nextLayer:string}) => m(this.WARN_TouchLayoutMissingLayer,
     `Key "${o.keyId}" on platform "${o.platformName}", layer "${o.layerId}", references a missing layer "${o.nextLayer}"`);
+
   static Warn_TouchLayoutUnidentifiedKey = (o:{layerId:string}) => m(this.WARN_TouchLayoutUnidentifiedKey,
     `A key on layer "${o.layerId}" has no identifier.`);
+
   static Error_TouchLayoutInvalidIdentifier = (o:{keyId:string, platformName: string, layerId:string}) => m(this.ERROR_TouchLayoutInvalidIdentifier,
     `Key "${o.keyId}" on "${o.platformName}", layer "${o.layerId}" has an invalid identifier.`);
+
   static Warn_TouchLayoutCustomKeyNotDefined = (o:{keyId:string, platformName:string, layerId:string}) => m(this.WARN_TouchLayoutCustomKeyNotDefined,
     `Key "${o.keyId}" on platform "${o.platformName}", layer "${o.layerId}", is a custom key but has no corresponding rule in the source.`);
-  static Warn_TouchLayoutSpecialLabelOnNormalKey = (o:{keyId:string, platformName:string, layerId:string, label:string}) => m(this.WARN_TouchLayoutSpecialLabelOnNormalKey,
-    `Key "${o.keyId}" on platform "${o.platformName}", layer "${o.layerId}" does not have the key type "Special" or "Special (active)" but has the label "${o.label}". This feature is only supported in Keyman 14 or later`);
+
+  static Warn_TouchLayoutSpecialLabelOnNormalKey = (o:{keyId:string, platformName:string, layerId:string, label:string}) =>
+    m(this.WARN_TouchLayoutSpecialLabelOnNormalKey,
+    `Key "${o.keyId}" on platform "${o.platformName}", layer "${o.layerId}" does not have `+
+    `the key type "Special" or "Special (active)" but has the label "${o.label}". This feature is only supported in Keyman 14 or later`);
+
   static Error_InvalidKeyCode = (o:{keyId: string}) => m(this.ERROR_InvalidKeyCode,
     `Invalid key identifier "${o.keyId}"`);
+
   static Warn_TouchLayoutFontShouldBeSameForAllPlatforms = () => m(this.WARN_TouchLayoutFontShouldBeSameForAllPlatforms,
     `The touch layout font should be the same for all platforms.`);
+
   static Warn_TouchLayoutMissingRequiredKeys = (o:{layerId:string, platformName:string, missingKeys:string}) => m(this.WARN_TouchLayoutMissingRequiredKeys,
     `Layer "${o.layerId}" on platform "${o.platformName}" is missing the required key(s) '${o.missingKeys}'.`);
 
diff --git a/developer/src/kmc-kmn/test/fixtures/invalid-keyboards/error_not_supported_in_keyman_web_output.kmn b/developer/src/kmc-kmn/test/fixtures/invalid-keyboards/error_not_supported_in_keyman_web_output.kmn
new file mode 100644
index 0000000000..cd2c34bb64
--- /dev/null
+++ b/developer/src/kmc-kmn/test/fixtures/invalid-keyboards/error_not_supported_in_keyman_web_output.kmn
@@ -0,0 +1,11 @@
+c Tests ERROR_NotSupportedInKeymanWebOutput for `return`
+
+store(&NAME) 'ERROR_NotSupportedInKeymanWebOutput'
+store(&VERSION) '9.0'
+store(&TARGETS) 'web'
+
+begin unicode > use(main)
+
+group(main) using keys
+
++ 'a' > return
diff --git a/developer/src/kmc-kmn/test/test-messages.ts b/developer/src/kmc-kmn/test/test-messages.ts
index 0220c2d037..af07abc2ad 100644
--- a/developer/src/kmc-kmn/test/test-messages.ts
+++ b/developer/src/kmc-kmn/test/test-messages.ts
@@ -80,4 +80,11 @@ describe('CompilerMessages', function () {
     assert.equal(callbacks.messages[0].message, "A key on layer \"default\" has no identifier.");
   });
 
+  // ERROR_NotSupportedInKeymanWebOutput
+
+  it('should generate ERROR_NotSupportedInKeymanWebOutput if a rule has `return` in the output', async function() {
+    await testForMessage(this, ['invalid-keyboards', 'error_not_supported_in_keyman_web_output.kmn'], KmnCompilerMessages.ERROR_NotSupportedInKeymanWebOutput);
+    assert.equal(callbacks.messages[0].message, "Statement \"return\" is not currently supported in output");
+  });
+
 });