diff --git a/compress.c b/compress.c
index 5dfa002..2dc5dc1 100644
--- a/compress.c
+++ b/compress.c
@@ -321,7 +321,7 @@
    ---*/
    for (iter = 0; iter < BZ_N_ITERS; iter++) {
 
-      for (t = 0; t < nGroups; t++) fave[t] = 0;
+      for (t = 0; t < BZ_N_GROUPS; t++) fave[t] = 0;
 
       for (t = 0; t < nGroups; t++)
          for (v = 0; v < alphaSize; v++)
@@ -353,7 +353,7 @@
             Calculate the cost of this group as coded
             by each of the coding tables.
          --*/
-         for (t = 0; t < nGroups; t++) cost[t] = 0;
+         for (t = 0; t < BZ_N_GROUPS; t++) cost[t] = 0;
 
          if (nGroups == 6 && 50 == ge-gs+1) {
             /*--- fast track the common case ---*/