diff --git a/compatibility_matrices/compatibility_matrix.mk b/compatibility_matrices/compatibility_matrix.mk
index 14c60ab..96815b8 100644
--- a/compatibility_matrices/compatibility_matrix.mk
+++ b/compatibility_matrices/compatibility_matrix.mk
@@ -78,7 +78,7 @@
 
 $(GEN): PRIVATE_SRC_FILES := $(my_matrix_src_files)
 $(GEN): $(my_matrix_src_files) $(HOST_OUT_EXECUTABLES)/assemble_vintf
-	$(foreach varname,$(PRIVATE_ENV_VARS),$(varname)=$($(varname))) \
+	$(foreach varname,$(PRIVATE_ENV_VARS),$(varname)="$($(varname))") \
 		$(HOST_OUT_EXECUTABLES)/assemble_vintf \
 		-i $(call normalize-path-list,$(PRIVATE_SRC_FILES)) \
 		-o $@ \