diff --git a/thermion_dart/native/include/c_api/APIBoundaryTypes.h b/thermion_dart/native/include/c_api/APIBoundaryTypes.h
index 764e49aa..86a5da68 100644
--- a/thermion_dart/native/include/c_api/APIBoundaryTypes.h
+++ b/thermion_dart/native/include/c_api/APIBoundaryTypes.h
@@ -166,18 +166,10 @@ extern "C"
 		PRIMITIVETYPE_TRIANGLE_STRIP = 5     //!< triangle strip
 	};
 
-	extern uint64_t TSWAP_CHAIN_CONFIG_TRANSPARENT;
-	extern uint64_t TSWAP_CHAIN_CONFIG_READABLE;
-	extern uint64_t TSWAP_CHAIN_CONFIG_APPLE_CVPIXELBUFFER;
-	extern uint64_t TSWAP_CHAIN_CONFIG_HAS_STENCIL_BUFFER;
-
-	extern uint64_t TSWAP_CHAIN_CONFIG_TRANSPARENT;
-	extern uint64_t TSWAP_CHAIN_CONFIG_READABLE;
-	extern uint64_t TSWAP_CHAIN_CONFIG_APPLE_CVPIXELBUFFER;
-	extern uint64_t TSWAP_CHAIN_CONFIG_HAS_STENCIL_BUFFER;
-
-
-
+	EMSCRIPTEN_KEEPALIVE extern uint64_t TSWAP_CHAIN_CONFIG_TRANSPARENT;
+	EMSCRIPTEN_KEEPALIVE extern uint64_t TSWAP_CHAIN_CONFIG_READABLE;
+	EMSCRIPTEN_KEEPALIVE extern uint64_t TSWAP_CHAIN_CONFIG_APPLE_CVPIXELBUFFER;
+	EMSCRIPTEN_KEEPALIVE extern uint64_t TSWAP_CHAIN_CONFIG_HAS_STENCIL_BUFFER;
 
 #ifdef __cplusplus
 }