diff --git a/cpp/src/Slice/Grammar.cpp b/cpp/src/Slice/Grammar.cpp
index c9a3c6844b4..befc734acdd 100644
--- a/cpp/src/Slice/Grammar.cpp
+++ b/cpp/src/Slice/Grammar.cpp
@@ -1884,7 +1884,7 @@ yyparse(void)
             size_t startPos = 0;
             if (ident->v.find("::") == 0)
             {
-                currentUnit->error("module identifiers cannot start with '::' prefix");
+                currentUnit->error("illegal identifier: module identifiers cannot start with '::' prefix");
                 startPos += 2; // Skip the leading "::".
             }
 
diff --git a/cpp/src/Slice/Grammar.y b/cpp/src/Slice/Grammar.y
index e9975d847ca..0cd83144d59 100644
--- a/cpp/src/Slice/Grammar.y
+++ b/cpp/src/Slice/Grammar.y
@@ -393,7 +393,7 @@ module_def
     size_t startPos = 0;
     if (ident->v.find("::") == 0)
     {
-        currentUnit->error("module identifiers cannot start with '::' prefix");
+        currentUnit->error("illegal identifier: module identifiers cannot start with '::' prefix");
         startPos += 2; // Skip the leading "::".
     }
 
diff --git a/cpp/test/Slice/errorDetection/NestedModule.err b/cpp/test/Slice/errorDetection/NestedModule.err
index d7f94cf5e7d..c512ae124a0 100644
--- a/cpp/test/Slice/errorDetection/NestedModule.err
+++ b/cpp/test/Slice/errorDetection/NestedModule.err
@@ -6,5 +6,5 @@ NestedModule.ice:20: illegal identifier `Holder': `Holder' suffix is reserved
 NestedModule.ice:24: illegal identifier `APtr': `Ptr' suffix is reserved
 NestedModule.ice:24: illegal identifier `BPrx': `Prx' suffix is reserved
 NestedModule.ice:24: illegal identifier `CHelper': `Helper' suffix is reserved
-NestedModule.ice:27: missing identifier: illegal empty identifier
+NestedModule.ice:27: illegal identifier: module identifiers cannot start with '::' prefix
 NestedModule.ice:27: illegal identifier `Helper': `Helper' suffix is reserved