diff --git a/BUILD.gn b/BUILD.gn
index 29256c4..a23ff96 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -246,6 +246,8 @@
       ]
     }
 
+    include_dirs = [ "${target_gen_dir}/include" ]
+
     deps = [ ":glslang_build_info" ]
 
     if (invoker.enable_opt) {
@@ -253,10 +255,9 @@
         "${spirv_tools_dir}:spvtools_opt",
         "${spirv_tools_dir}:spvtools_val",
       ]
+      include_dirs += [ "${spirv_tools_dir}/include" ]
     }
 
-    include_dirs = [ "${target_gen_dir}/include" ]
-
     configs -= _configs_to_remove
     configs += _configs_to_add
   }
@@ -302,7 +303,10 @@
   ]
   public_configs = [ ":glslang_hlsl" ]
 
-  include_dirs = [ "${target_gen_dir}/include" ]
+  include_dirs = [
+    "${target_gen_dir}/include",
+    "${spirv_tools_dir}/include",
+  ]
 
   configs -= _configs_to_remove
   configs += _configs_to_add
@@ -313,6 +317,8 @@
   defines = [ "ENABLE_OPT=1" ]
   deps = [ ":glslang_sources" ]
 
+  include_dirs += [ "${spirv_tools_dir}/include" ]
+
   configs -= _configs_to_remove
   configs += _configs_to_add
 }