diff --git a/glslang/CInterface/glslang_c_interface.cpp b/glslang/CInterface/glslang_c_interface.cpp
index 1465ce17..870698f2 100644
--- a/glslang/CInterface/glslang_c_interface.cpp
+++ b/glslang/CInterface/glslang_c_interface.cpp
@@ -80,25 +80,6 @@ typedef struct glslang_program_s {
    (CallbackIncluder::callbacks::free_include_result)
 */
 class CallbackIncluder : public glslang::TShader::Includer {
-public:
-    /* Wrapper of IncludeResult which stores a glsl_include_result object internally */
-    class CallbackIncludeResult : public glslang::TShader::Includer::IncludeResult {
-    public:
-        CallbackIncludeResult(const std::string& headerName, const char* const headerData, const size_t headerLength,
-                              void* userData, glsl_include_result_t* includeResult)
-            : glslang::TShader::Includer::IncludeResult(headerName, headerData, headerLength, userData),
-              includeResult(includeResult)
-        {
-        }
-
-        virtual ~CallbackIncludeResult() {}
-
-    protected:
-        friend class CallbackIncluder;
-
-        glsl_include_result_t* includeResult;
-    };
-
 public:
     CallbackIncluder(glsl_include_callbacks_t _callbacks, void* _context) : callbacks(_callbacks), context(_context) {}
 
@@ -110,9 +91,7 @@ public:
         if (this->callbacks.include_system) {
             glsl_include_result_t* result =
                 this->callbacks.include_system(this->context, headerName, includerName, inclusionDepth);
-
-            return new CallbackIncludeResult(std::string(headerName), result->header_data, result->header_length,
-                                             nullptr, result);
+            return makeIncludeResult(result);
         }
 
         return glslang::TShader::Includer::includeSystem(headerName, includerName, inclusionDepth);
@@ -124,9 +103,7 @@ public:
         if (this->callbacks.include_local) {
             glsl_include_result_t* result =
                 this->callbacks.include_local(this->context, headerName, includerName, inclusionDepth);
-
-            return new CallbackIncludeResult(std::string(headerName), result->header_data, result->header_length,
-                                             nullptr, result);
+            return makeIncludeResult(result);
         }
 
         return glslang::TShader::Includer::includeLocal(headerName, includerName, inclusionDepth);
@@ -139,22 +116,25 @@ public:
         if (result == nullptr)
             return;
 
-        if (this->callbacks.free_include_result && (result->userData == nullptr)) {
-            CallbackIncludeResult* innerResult = static_cast<CallbackIncludeResult*>(result);
-            /* use internal free() function */
-            this->callbacks.free_include_result(this->context, innerResult->includeResult);
-            /* ignore internal fields of TShader::Includer::IncludeResult */
-            delete result;
-            return;
+        if (this->callbacks.free_include_result) {
+            this->callbacks.free_include_result(this->context, static_cast<glsl_include_result_t*>(result->userData));
         }
 
-        delete[] static_cast<char*>(result->userData);
         delete result;
     }
 
 private:
     CallbackIncluder() {}
 
+    IncludeResult* makeIncludeResult(glsl_include_result_t* result) {
+        if (!result) {
+            return nullptr;
+        }
+
+        return new glslang::TShader::Includer::IncludeResult(
+            std::string(result->header_name), result->header_data, result->header_length, result);
+    }
+
     /* C callback pointers */
     glsl_include_callbacks_t callbacks;
     /* User-defined context */
@@ -394,8 +374,11 @@ GLSLANG_EXPORT const char* glslang_shader_get_preprocessed_code(glslang_shader_t
 
 GLSLANG_EXPORT int glslang_shader_preprocess(glslang_shader_t* shader, const glslang_input_t* input)
 {
-    DirStackFileIncluder Includer;
-    /* TODO: use custom callbacks if they are available in 'i->callbacks' */
+    DirStackFileIncluder dirStackFileIncluder;
+    CallbackIncluder callbackIncluder(input->callbacks, input->callbacks_ctx);
+    glslang::TShader::Includer& Includer = (input->callbacks.include_local||input->callbacks.include_system)
+        ? static_cast<glslang::TShader::Includer&>(callbackIncluder)
+        : static_cast<glslang::TShader::Includer&>(dirStackFileIncluder);
     return shader->shader->preprocess(
         reinterpret_cast<const TBuiltInResource*>(input->resource),
         input->default_version,
diff --git a/glslang/Include/glslang_c_interface.h b/glslang/Include/glslang_c_interface.h
index 28d52330..a519f635 100644
--- a/glslang/Include/glslang_c_interface.h
+++ b/glslang/Include/glslang_c_interface.h
@@ -168,23 +168,6 @@ typedef struct glslang_resource_s {
     glslang_limits_t limits;
 } glslang_resource_t;
 
-typedef struct glslang_input_s {
-    glslang_source_t language;
-    glslang_stage_t stage;
-    glslang_client_t client;
-    glslang_target_client_version_t client_version;
-    glslang_target_language_t target_language;
-    glslang_target_language_version_t target_language_version;
-    /** Shader source code */
-    const char* code;
-    int default_version;
-    glslang_profile_t default_profile;
-    int force_default_version_and_profile;
-    int forward_compatible;
-    glslang_messages_t messages;
-    const glslang_resource_t* resource;
-} glslang_input_t;
-
 /* Inclusion result structure allocated by C include_local/include_system callbacks */
 typedef struct glsl_include_result_s {
     /* Header file name or NULL if inclusion failed */
@@ -214,6 +197,25 @@ typedef struct glsl_include_callbacks_s {
     glsl_free_include_result_func free_include_result;
 } glsl_include_callbacks_t;
 
+typedef struct glslang_input_s {
+    glslang_source_t language;
+    glslang_stage_t stage;
+    glslang_client_t client;
+    glslang_target_client_version_t client_version;
+    glslang_target_language_t target_language;
+    glslang_target_language_version_t target_language_version;
+    /** Shader source code */
+    const char* code;
+    int default_version;
+    glslang_profile_t default_profile;
+    int force_default_version_and_profile;
+    int forward_compatible;
+    glslang_messages_t messages;
+    const glslang_resource_t* resource;
+    glsl_include_callbacks_t callbacks;
+    void* callbacks_ctx;
+} glslang_input_t;
+
 /* SpvOptions counterpart */
 typedef struct glslang_spv_options_s {
     bool generate_debug_info;