diff --git a/Test/150.frag b/Test/150.frag
index 16963afb..e87d6336 100644
--- a/Test/150.frag
+++ b/Test/150.frag
@@ -47,4 +47,5 @@ void barWxyz()
 int primitiveID()
 {
    return gl_PrimitiveID;
+   gl_PerFragment; // ERROR, block name can't get reused
 }
diff --git a/Test/baseResults/150.frag.out b/Test/baseResults/150.frag.out
index 1454b558..e51b13d1 100644
--- a/Test/baseResults/150.frag.out
+++ b/Test/baseResults/150.frag.out
@@ -3,7 +3,9 @@ ERROR: 0:4: 'redeclaration' : cannot redeclare with different qualification: gl_
 ERROR: 0:5: 'redeclaration' : cannot redeclare with different qualification: gl_FragCoord
 ERROR: 0:6: 'layout qualifier' : can only apply origin_upper_left and pixel_center_origin to gl_FragCoord 
 ERROR: 0:14: 'gl_FragCoord' : cannot redeclare after use 
-ERROR: 4 compilation errors.  No code generated.
+ERROR: 0:50: 'gl_PerFragment' : cannot be used (maybe an instance name is needed) 
+ERROR: 0:50: 'gl_PerFragment' : undeclared identifier 
+ERROR: 6 compilation errors.  No code generated.
 
 
 Shader version: 150
@@ -106,6 +108,7 @@ ERROR: node is still EOpNull!
 0:49    Sequence
 0:49      Branch: Return with expression
 0:49        'gl_PrimitiveID' ( flat in int PrimitiveID)
+0:50      'gl_PerFragment' ( temp float)
 0:?   Linker Objects
 0:?     'gl_FragCoord' ( gl_FragCoord 4-component vector of float FragCoord)
 0:?     'foo' ( smooth in 4-component vector of float)
diff --git a/glslang/Include/Types.h b/glslang/Include/Types.h
index 3140006e..a419cb0f 100644
--- a/glslang/Include/Types.h
+++ b/glslang/Include/Types.h
@@ -1661,6 +1661,8 @@ public:
     virtual bool isImage()   const { return basicType == EbtSampler && getSampler().isImage(); }
     virtual bool isSubpass() const { return basicType == EbtSampler && getSampler().isSubpass(); }
     virtual bool isTexture() const { return basicType == EbtSampler && getSampler().isTexture(); }
+    // Check the block-name convention of creating a block without populating it's members:
+    virtual bool isUnusableName() const { return isStruct() && structure == nullptr; }
     virtual bool isParameterized()  const { return typeParameters != nullptr; }
 #ifdef GLSLANG_WEB
     bool isAtomic() const { return false; }
diff --git a/glslang/MachineIndependent/ParseHelper.cpp b/glslang/MachineIndependent/ParseHelper.cpp
index 33a16641..08fa610c 100644
--- a/glslang/MachineIndependent/ParseHelper.cpp
+++ b/glslang/MachineIndependent/ParseHelper.cpp
@@ -319,10 +319,15 @@ TIntermTyped* TParseContext::handleVariable(const TSourceLoc& loc, TSymbol* symb
         // If this is a variable or a block, check it and all it contains, but if this
         // is a member of an anonymous block, check the whole block, as the whole block
         // will need to be copied up if it contains an unsized array.
-        if (symbol->getType().containsUnsizedArray() ||
-            (symbol->getAsAnonMember() &&
-             symbol->getAsAnonMember()->getAnonContainer().getType().containsUnsizedArray()))
-            makeEditable(symbol);
+        //
+        // This check is being done before the block-name check further down, so guard
+        // for that too.
+        if (!symbol->getType().isUnusableName()) {
+            if (symbol->getType().containsUnsizedArray() ||
+                (symbol->getAsAnonMember() &&
+                 symbol->getAsAnonMember()->getAnonContainer().getType().containsUnsizedArray()))
+                makeEditable(symbol);
+        }
     }
 #endif
 
@@ -347,8 +352,7 @@ TIntermTyped* TParseContext::handleVariable(const TSourceLoc& loc, TSymbol* symb
         // See if it was a variable.
         variable = symbol ? symbol->getAsVariable() : nullptr;
         if (variable) {
-            if ((variable->getType().getBasicType() == EbtBlock ||
-                 variable->getType().getBasicType() == EbtStruct) && variable->getType().getStruct() == nullptr) {
+            if (variable->getType().isUnusableName()) {
                 error(loc, "cannot be used (maybe an instance name is needed)", string->c_str(), "");
                 variable = nullptr;
             }