diff --git a/src/Parsee/Data.c b/src/Parsee/Data.c
index 9efcc5b..eca3725 100644
--- a/src/Parsee/Data.c
+++ b/src/Parsee/Data.c
@@ -155,7 +155,8 @@ XMPPifyElement(HashMap *event, XMLElement *elem, XMPPFlags flags)
 #define Concat(strp)    do \
                         { \
                             size_t cidx; \
-                            for (cidx = 0; cidx < strlen(strp); cidx++) \
+                            size_t len = strp ? strlen(strp) : 0; \
+                            for (cidx = 0; cidx < len; cidx++) \
                             { \
                                 char cch[2] = { strp[cidx], 0 }; \
                                 char nch = *cch ? strp[cidx+1] : '\0'; \