diff --git a/MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp b/MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp
index 4186cc58..d65a1db5 100644
--- a/MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp
+++ b/MobileGL/MG_Impl/GLImpl/Program/GL_Program.cpp
@@ -57,7 +57,19 @@ namespace MobileGL {
         }
 
         void AttachShader_State(GLuint program, GLuint shader) {
-            THROW_UNIMPL_EXCEPTION;
+            auto programObject = TryToGetProgramObject(program);
+            if (!programObject)
+                return;
+            auto shaderObject = TryToGetShaderObject(shader);
+            if (!shaderObject)
+                return;
+            if (!programObject->AttachShader(shaderObject)) {
+                MG_State::pGLContext->RecordError(
+                    ErrorCode::InvalidOperation,
+                    MakeShared<GenericErrorInfo>("MG_Impl/GLImpl", __func__,
+                                                 "`shader` is already attached to `program`."));
+                return;
+            }
         }
 
         void BindAttribLocation_State(GLuint program, GLuint index, const GLchar* name) {
diff --git a/MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp b/MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp
index 2f58b2b7..a82c57a9 100644
--- a/MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp
+++ b/MobileGL/MG_State/GLState/ProgramState/ProgramObject.cpp
@@ -4,8 +4,19 @@
 namespace MobileGL {
     namespace MG_State {
         namespace GLState {
-            void ProgramObject::AttachShader(SharedPtr<ShaderObject> shader) {
+            bool ProgramObject::ShaderIsAttached(SharedPtr<ShaderObject> shader) {
+                auto it = std::find_if(m_shaders.begin(), m_shaders.end(),
+                    [shader](const SharedPtr<ShaderObject>& s) {
+                        return s.get() == shader.get();
+                    });
+                return it != m_shaders.end();
+            }
+
+            bool ProgramObject::AttachShader(SharedPtr<ShaderObject> shader) {
+                if (ShaderIsAttached(shader))
+                    return false;
                 m_shaders.emplace_back(shader);
+                return true;
             }
 
             SizeT ProgramObject::DetachShader(SharedPtr<ShaderObject> shader) {
diff --git a/MobileGL/MG_State/GLState/ProgramState/ProgramObject.h b/MobileGL/MG_State/GLState/ProgramState/ProgramObject.h
index 2d2819a5..1946707d 100644
--- a/MobileGL/MG_State/GLState/ProgramState/ProgramObject.h
+++ b/MobileGL/MG_State/GLState/ProgramState/ProgramObject.h
@@ -7,7 +7,8 @@ namespace MobileGL {
         namespace GLState {
             class ProgramObject {
             public:
-                void AttachShader(SharedPtr<ShaderObject> shader);
+                bool ShaderIsAttached(SharedPtr<ShaderObject> shader);
+                bool AttachShader(SharedPtr<ShaderObject> shader);
                 SizeT DetachShader(SharedPtr<ShaderObject> shader);
                 void Link();
                 void MarkAsDeleted();