diff --git a/include/lbfgs.h b/include/lbfgs.h
index c41a939..eeb6f02 100644
--- a/include/lbfgs.h
+++ b/include/lbfgs.h
@@ -74,6 +74,8 @@ enum {
     LBFGSFALSE = 0,
     /** True value. */
     LBFGSTRUE,
+    /** */
+    LBFGS_ALREADY_MINIMIZED,
 
     /** Unknown error. */
     LBFGSERR_UNKNOWNERROR = -1024,
diff --git a/lib/lbfgs.c b/lib/lbfgs.c
index 342c0f5..27af73c 100644
--- a/lib/lbfgs.c
+++ b/lib/lbfgs.c
@@ -184,7 +184,7 @@ lbfgsfloatval_t* lbfgs_malloc(int n)
 #if     defined(USE_SSE) && (defined(__SSE__) || defined(__SSE2__))
     n = round_out_variables(n);
 #endif/*defined(USE_SSE)*/
-    return vecalloc(sizeof(lbfgsfloatval_t) * n);
+    return (lbfgsfloatval_t*)vecalloc(sizeof(lbfgsfloatval_t) * n);
 }
 
 void lbfgs_free(lbfgsfloatval_t *x)
@@ -354,6 +354,15 @@ int lbfgs(
         }
     }
 
+    /*
+       Make sure that the gradients are not zero.
+     */
+    vecnorm(&gnorm, g, n);
+    if (gnorm == 0.) {
+        ret = LBFGS_ALREADY_MINIMIZED;
+        goto lbfgs_exit;
+    }
+
     /* Compute the initial step:
         step = 1.0 / sqrt(vecdot(d, d, n))
      */