diff --git a/src/d_deh.c b/src/d_deh.c
index f95f55f5cf..155c43bca8 100644
--- a/src/d_deh.c
+++ b/src/d_deh.c
@@ -4071,7 +4071,7 @@ static void deh_procStrings(DEHFILE *fpin, const char *line)
         while (strlen(holdstring) + len > (unsigned int)maxstrlen)
         {
             // killough 11/98: allocate enough the first time
-            maxstrlen = (int)strlen(holdstring) + len;
+            maxstrlen = (int)strlen(holdstring) + len + 1;
 
             if (devparm)
                 C_Output("* increased buffer from to %i for buffer size %i", maxstrlen, len);