diff --git a/src/pageEditor/hooks/useBuildAndValidateMod.ts b/src/pageEditor/hooks/useBuildAndValidateMod.ts
index cbc7f82ad6..2083efcf6d 100644
--- a/src/pageEditor/hooks/useBuildAndValidateMod.ts
+++ b/src/pageEditor/hooks/useBuildAndValidateMod.ts
@@ -80,37 +80,33 @@ function useBuildAndValidateMod(): UseBuildAndValidateModReturn {
         dirtyModMetadata,
       });
 
-      if (sourceMod != null) {
-        const modComponentDefinitionCountsMatch =
-          compareModComponentCountsToModDefinition(newMod, {
-            sourceModDefinition: sourceMod,
-            newModComponentFormState,
-          });
+      const modComponentDefinitionCountsMatch =
+        compareModComponentCountsToModDefinition(newMod, {
+          sourceModDefinition: sourceMod,
+          newModComponentFormState,
+        });
 
-        const modComponentStarterBricksMatch =
-          await checkModStarterBrickInvariants(newMod, {
-            sourceModDefinition: sourceMod,
-            newModComponentFormState,
-          });
+      const modComponentStarterBricksMatch =
+        await checkModStarterBrickInvariants(newMod, {
+          sourceModDefinition: sourceMod,
+          newModComponentFormState,
+        });
 
-        if (
-          !modComponentDefinitionCountsMatch ||
-          !modComponentStarterBricksMatch
-        ) {
-          // Not including modDefinition because it can be 1.5MB+ in some rare cases
-          // See discussion: https://github.com/pixiebrix/pixiebrix-extension/pull/7629/files#r1492864349
-          reportEvent(Events.PAGE_EDITOR_MOD_SAVE_ERROR, {
-            // Metadata is an object, but doesn't extend JsonObject so typescript doesn't like it
-            modMetadata: newMod.metadata as unknown as JsonObject,
-            modComponentDefinitionCountsMatch,
-            modComponentStarterBricksMatch,
-          });
-          dispatch(editorActions.showSaveDataIntegrityErrorModal());
+      if (
+        !modComponentDefinitionCountsMatch ||
+        !modComponentStarterBricksMatch
+      ) {
+        // Not including modDefinition because it can be 1.5MB+ in some rare cases
+        // See discussion: https://github.com/pixiebrix/pixiebrix-extension/pull/7629/files#r1492864349
+        reportEvent(Events.PAGE_EDITOR_MOD_SAVE_ERROR, {
+          // Metadata is an object, but doesn't extend JsonObject so typescript doesn't like it
+          modMetadata: newMod.metadata as unknown as JsonObject,
+          modComponentDefinitionCountsMatch,
+          modComponentStarterBricksMatch,
+        });
+        dispatch(editorActions.showSaveDataIntegrityErrorModal());
 
-          throw new BusinessError(
-            "Mod save failed due to data integrity error",
-          );
-        }
+        throw new BusinessError("Mod save failed due to data integrity error");
       }
 
       return newMod;
diff --git a/src/pageEditor/hooks/useCompareModComponentCounts.ts b/src/pageEditor/hooks/useCompareModComponentCounts.ts
index 3a606fe43d..3bf4f0b087 100644
--- a/src/pageEditor/hooks/useCompareModComponentCounts.ts
+++ b/src/pageEditor/hooks/useCompareModComponentCounts.ts
@@ -29,16 +29,12 @@ type SourceModParts = {
   newModComponentFormState?: ModComponentFormState;
 };
 
-type RequiredModParts = Required<
-  Pick<SourceModParts, "sourceModDefinition" | "newModComponentFormState">
->;
-
 /**
  * @returns A function that compares the number of mod components in the redux state and the mod definition
  */
 function useCompareModComponentCounts(): (
   unsavedModDefinition: UnsavedModDefinition,
-  { sourceModDefinition, newModComponentFormState }: RequiredModParts,
+  { sourceModDefinition, newModComponentFormState }: SourceModParts,
 ) => boolean {
   const getCleanComponentsAndDirtyFormStatesForMod = useSelector(
     selectGetCleanComponentsAndDirtyFormStatesForMod,
@@ -47,9 +43,13 @@ function useCompareModComponentCounts(): (
   return useCallback(
     (
       unsavedModDefinition: UnsavedModDefinition,
-      { sourceModDefinition, newModComponentFormState }: RequiredModParts,
+      { sourceModDefinition, newModComponentFormState }: SourceModParts,
     ) => {
-      const modId = sourceModDefinition.metadata.id;
+      // Always compare to the pre-existing mod if it exists
+      const modId = sourceModDefinition
+        ? sourceModDefinition.metadata.id
+        : // See useCreateModFromModComponent.ts for an example where there is no sourceModDefinition
+          unsavedModDefinition.metadata.id;
       const { cleanModComponents, dirtyModComponentFormStates } =
         getCleanComponentsAndDirtyFormStatesForMod(modId);