diff --git a/share/analysis-scripts/frama-c.mk b/share/analysis-scripts/frama-c.mk
index 3da9f1cf65582a904f5e2903fb7f0cf3adffa336..ee3b6d3d43ae77d30ff499227c140a1497cec166 100644
--- a/share/analysis-scripts/frama-c.mk
+++ b/share/analysis-scripts/frama-c.mk
@@ -92,8 +92,8 @@ define display_command =
   $(info )
 endef
 
-space :=
-space +=
+empty :=
+space := $(empty) $(empty)
 comma := ,
 
 fc_list = $(subst $(space),$(comma),$(strip $1))