diff --git a/external/libgltf/ExternalProject_libgltf.mk b/external/libgltf/ExternalProject_libgltf.mk
index 580c0102889d..5c40aa727ca6 100644
--- a/external/libgltf/ExternalProject_libgltf.mk
+++ b/external/libgltf/ExternalProject_libgltf.mk
@@ -39,6 +39,9 @@ ifeq ($(SYSTEM_GLM),)
 libgltf_AdditionalIncludes += "$(call gb_UnpackedTarball_get_dir,glm)"
 endif
 
+libgltf_empty :=
+libgltf_space := $(libgltf_empty) $(libgltf_empty)
+
 $(call gb_ExternalProject_get_state_target,libgltf,build) :
 	$(call gb_ExternalProject_run,build,\
 		msbuild.exe libgltf.vcxproj \
@@ -47,7 +50,7 @@ $(call gb_ExternalProject_get_state_target,libgltf,build) :
 				/p:VisualStudioVersion=11.0) \
 			$(if $(filter 100,$(VCVER)),/p:PlatformToolset=v100 \
 				/p:VisualStudioVersion=10.0) \
-			'/p:AdditionalIncludeDirectories=$(subst $(gb_SPACE),;,$(subst /,\,$(strip $(libgltf_AdditionalIncludes))))' \
+			'/p:AdditionalIncludeDirectories=$(subst $(libgltf_space),;,$(subst /,\,$(strip $(libgltf_AdditionalIncludes))))' \
 			/p:AdditionalLibraryDirectories=$(if $(SYSTEM_GLEW),,"$(subst /,\,$(call gb_UnpackedTarball_get_dir,glew))\lib\$(if $(MSVC_USE_DEBUG_RUNTIME),Debug,Release)\Win32") \
 	,build/win32)