diff --git a/recipes-isdn/libgsm/libgsm_1.0.13.bb b/recipes-isdn/libgsm/libgsm_1.0.13.bb
index b26f587578..e6bf9baf60 100644
--- a/recipes-isdn/libgsm/libgsm_1.0.13.bb
+++ b/recipes-isdn/libgsm/libgsm_1.0.13.bb
@@ -1,6 +1,6 @@
 require libgsm.inc
 
-PR = ${INC_PR}.0
+PR = "${INC_PR}.0"
 
 S = "${WORKDIR}/gsm-1.0-pl13/"