diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index 37313fd0..d133b594 100644
--- a/StandAlone/StandAlone.cpp
+++ b/StandAlone/StandAlone.cpp
@@ -582,7 +582,7 @@ void CompileAndLinkShaderUnits(std::vector<ShaderCompUnit> compUnits)
 
         if (Options & EOptionOutputPreprocessed) {
             std::string str;
-            glslang::TShader::Includer includer;
+            glslang::TShader::ForbidIncluder includer;
             if (shader->preprocess(&Resources, defaultVersion, ENoProfile, false, false,
                                    messages, &str, includer)) {
                 PutsIfNonEmpty(str.c_str());
diff --git a/glslang/MachineIndependent/ShaderLang.cpp b/glslang/MachineIndependent/ShaderLang.cpp
index ac1156e4..321940a6 100644
--- a/glslang/MachineIndependent/ShaderLang.cpp
+++ b/glslang/MachineIndependent/ShaderLang.cpp
@@ -221,7 +221,7 @@ bool InitializeSymbolTable(const TString& builtIns, int version, EProfile profil
                                                                        language, infoSink, spvVersion, true, EShMsgDefault,
                                                                        true));
 
-    TShader::Includer includer;
+    TShader::ForbidIncluder includer;
     TPpContext ppContext(*parseContext, "", includer);
     TScanContext scanContext(*parseContext);
     parseContext->setScanContext(&scanContext);
@@ -1217,7 +1217,7 @@ int ShCompile(
     compiler->infoSink.debug.erase();
 
     TIntermediate intermediate(compiler->getLanguage());
-    TShader::Includer includer;
+    TShader::ForbidIncluder includer;
     bool success = CompileDeferred(compiler, shaderStrings, numStrings, inputLengths, nullptr,
                                    "", optLevel, resources, defaultVersion, ENoProfile, false,
                                    forwardCompatible, messages, intermediate, includer);
diff --git a/glslang/MachineIndependent/preprocessor/Pp.cpp b/glslang/MachineIndependent/preprocessor/Pp.cpp
index 411806f4..49c78ef8 100644
--- a/glslang/MachineIndependent/preprocessor/Pp.cpp
+++ b/glslang/MachineIndependent/preprocessor/Pp.cpp
@@ -576,12 +576,12 @@ int TPpContext::CPPifdef(int defined, TPpToken* ppToken)
 int TPpContext::CPPinclude(TPpToken* ppToken)
 {
     const TSourceLoc directiveLoc = ppToken->loc;
-    bool addLocalSearch = true; // to additionally include the extra "" paths
+    bool startWithLocalSearch = true; // to additionally include the extra "" paths
     int token = scanToken(ppToken);
 
     // handle <header-name>-style #include
     if (token == '<') {
-        addLocalSearch = false;
+        startWithLocalSearch = false;
         token = scanHeaderName(ppToken, '>');
     }
     // otherwise ppToken already has the header name and it was "header-name" style
@@ -609,7 +609,7 @@ int TPpContext::CPPinclude(TPpToken* ppToken)
     // Find the inclusion, first look in "Local" ("") paths, if requested,
     // otherwise, only search the "System" (<>) paths.
     TShader::Includer::IncludeResult* res = nullptr;
-    if (addLocalSearch)
+    if (startWithLocalSearch)
         res = includer.includeLocal(filename.c_str(), currentSourceFile.c_str(), includeStack.size() + 1);
     if (! res || res->headerName.empty()) {
         includer.releaseInclude(res);
diff --git a/glslang/Public/ShaderLang.h b/glslang/Public/ShaderLang.h
index 4b3b1f60..60e539b4 100644
--- a/glslang/Public/ShaderLang.h
+++ b/glslang/Public/ShaderLang.h
@@ -360,9 +360,11 @@ public:
         // Resolves an inclusion request by name, current source name,
         // and include depth.
         // On success, returns an IncludeResult containing the resolved name
-        // and content of the include.  On failure, returns an IncludeResult
+        // and content of the include.
+        // On failure, returns a nullptr, or an IncludeResult
         // with an empty string for the headerName and error details in the
-        // header field.  The Includer retains ownership of the contents
+        // header field.
+        // The Includer retains ownership of the contents
         // of the returned IncludeResult value, and those contents must
         // remain valid until the releaseInclude method is called on that
         // IncludeResult object.
@@ -385,14 +387,20 @@ public:
 
         // Signals that the parser will no longer use the contents of the
         // specified IncludeResult.
-        virtual void releaseInclude(IncludeResult* result) { }
+        virtual void releaseInclude(IncludeResult*) = 0;
         virtual ~Includer() {}
     };
 
+    // Fail all Includer searches
+    class ForbidIncluder : public Includer {
+    public:
+        virtual void releaseInclude(IncludeResult*) override { }
+    };
+
     bool parse(const TBuiltInResource* res, int defaultVersion, EProfile defaultProfile, bool forceDefaultVersionAndProfile,
                bool forwardCompatible, EShMessages messages)
     {
-        TShader::Includer includer;
+        TShader::ForbidIncluder includer;
         return parse(res, defaultVersion, defaultProfile, forceDefaultVersionAndProfile, forwardCompatible, messages, includer);
     }
 
diff --git a/gtests/TestFixture.h b/gtests/TestFixture.h
index ea377141..6f4afc66 100644
--- a/gtests/TestFixture.h
+++ b/gtests/TestFixture.h
@@ -521,7 +521,7 @@ public:
         glslang::TShader shader(EShLangVertex);
         shader.setStringsWithLengths(&shaderStrings, &shaderLengths, 1);
         std::string ppShader;
-        glslang::TShader::Includer includer;
+        glslang::TShader::ForbidIncluder includer;
         const bool success = shader.preprocess(
             &glslang::DefaultTBuiltInResource, defaultVersion, defaultProfile,
             forceVersionProfile, isForwardCompatible, (EShMessages)(EShMsgOnlyPreprocessor | EShMsgCascadingErrors),