diff --git a/src/xspice/icm/GNUmakefile.in b/src/xspice/icm/GNUmakefile.in
index 632c4d140..b2764ab57 100644
--- a/src/xspice/icm/GNUmakefile.in
+++ b/src/xspice/icm/GNUmakefile.in
@@ -46,7 +46,7 @@ clean:
 NGSRCDIR = $(srcdir)/../../
 
 dstring.o : $(NGSRCDIR)/misc/dstring.c $(NGSRCDIR)/include/ngspice/dstring.h
-	$(COMPILE) -I $(NGSRCDIR)/include/ngspice -o $@ -c $<
+	$(COMPILE) -I$(NGSRCDIR)/include/ngspice -o $@ -c $<
 
 ifdef cm