diff --git a/C/cmppreds.c b/C/cmppreds.c
index 4b833a0e0..fcdb8fff8 100644
--- a/C/cmppreds.c
+++ b/C/cmppreds.c
@@ -57,6 +57,8 @@ cmp_atoms(Atom a1, Atom a2)
 
       while (*s1 == *s2) {
 	if (!*s1) return 0;
+	s1++;
+	s2++;
       }
       return *s1-*s2;
     }
@@ -67,6 +69,8 @@ cmp_atoms(Atom a1, Atom a2)
 
     while (*s1 == *s2) {
       if (!*s1) return 0;
+      s1++;
+      s2++;
     }
     return *s1-*s2;
   } else {