--- old/make/copy/CopyCommon.gmk	2019-02-15 10:58:28.019298952 -0800
+++ new/make/copy/CopyCommon.gmk	2019-02-15 10:58:27.587284284 -0800
@@ -75,10 +75,12 @@
 define SetupCopyLegalFilesBody
   $$(foreach f, $$(filter-out $$(addprefix %/, $$($1_EXCLUDES)), \
       $$(wildcard $$(addsuffix /*, $$(call FindModuleLegalSrcDirs, $$(MODULE))))), \
-    $$(eval $$(call SetupCopyFiles, $1_$$(notdir $$f), \
-        DEST := $$(LEGAL_DST_DIR), \
-        FILES := $$f, \
-    )) \
-    $$(eval $1 += $$($1_$$(notdir $$f))) \
+    $$(if $$(filter $$($1_$$(notdir $$f)), $$($1)), , \
+      $$(eval $$(call SetupCopyFiles, $1_$$(notdir $$f), \
+          DEST := $$(LEGAL_DST_DIR), \
+          FILES := $$f, \
+      )) \
+      $$(eval $1 += $$($1_$$(notdir $$f))) \
+    ) \
   )
 endef