diff --git a/lib/decryption/a5_1_2.h b/lib/decryption/a5_1_2.h
index fb87498..75277df 100644
--- a/lib/decryption/a5_1_2.h
+++ b/lib/decryption/a5_1_2.h
@@ -364,13 +364,13 @@
   }
 }
 
-void runA51(unsigned char AtoBkeystream[]) {
+void runA51(byte AtoBkeystream[], byte BtoAkeystream[]) {
   int i;
 
   /* Zero out the output buffers. */
-  for (i = 0; i < 114; i++)
+  for (i = 0; i < 114; i++){
     AtoBkeystream[i] = 0;
-
+  }
 
   /* Generate 114 bits of keystream for the
    * A->B direction.  Store it, MSB first. */
@@ -378,6 +378,13 @@
     clock(0, 0);
     AtoBkeystream[i] = getbit();
   }
+  
+  /* Generate 114 bits of keystream for the
+   * B->A direction.  Store it, MSB first. */
+  for (i = 0; i < 114; i++) {
+    clock(0, 0);
+    BtoAkeystream[i] = getbit();
+  }
 }