diff --git a/sofort/cfgtest.sh b/sofort/cfgtest.sh
index 77ce1ea..a0dcc64 100644
--- a/sofort/cfgtest.sh
+++ b/sofort/cfgtest.sh
@@ -106,8 +106,8 @@ cfgtest_header_presence()
 		> /dev/null 2>/dev/null     \
 	|| return
 
-	mb_internal_str=$(printf '%s%s' '-DHAVE_' "$@"  \
-			| sed -e 's/\./_/g'             \
+	mb_internal_str=$(printf '%s%s' '-DHAVE_' "$@"    \
+			| sed -e 's/\./_/g' -e 's@/@_@g'  \
 			| tr "[:lower:]" "[:upper:]")
 
 	cfgtest_cflags_append "$mb_internal_str"
@@ -124,7 +124,7 @@ cfgtest_header_absence()
 	&& return
 
 	mb_internal_str=$(printf '%s%s' '-DHAVE_NO_' "$@" \
-			| sed -e 's/\./_/g'               \
+			| sed -e 's/\./_/g' -e 's@/@_@g'  \
 			| tr "[:lower:]" "[:upper:]")
 
 	cfgtest_cflags_append "$mb_internal_str"