diff --git a/library/bignum.c b/library/bignum.c
index 1422d5026..504f51bd4 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -1480,7 +1480,7 @@ int mpi_exp_mod( mpi *X, const mpi *A, const mpi *E, const mpi *N, mpi *_RR )
 
         for( i = 0; i < wsize - 1; i++ )
             mpi_montmul( &W[j], &W[j], N, mm, &T );
-    
+
         /*
          * W[i] = W[i - 1] * W[1]
          */
@@ -1503,9 +1503,11 @@ int mpi_exp_mod( mpi *X, const mpi *A, const mpi *E, const mpi *N, mpi *_RR )
     {
         if( bufsize == 0 )
         {
-            if( nblimbs-- == 0 )
+            if( nblimbs == 0 )
                 break;
 
+            nblimbs--;
+
             bufsize = sizeof( t_uint ) << 3;
         }