diff --git a/src/algs/slsqp/slsqp.c b/src/algs/slsqp/slsqp.c
index f572c8f1..d75f4a9b 100644
--- a/src/algs/slsqp/slsqp.c
+++ b/src/algs/slsqp/slsqp.c
@@ -2459,6 +2459,12 @@ nlopt_result nlopt_slsqp(unsigned n, nlopt_func f, void *f_data,
      unsigned max_cdim;
      int want_grad = 1;
      
+     if (p > n)
+     {
+       nlopt_stop_msg(stop, "slsqp: more equality constraints than variables");
+       ret = NLOPT_INVALID_ARGS;
+     }
+
      max_cdim = MAX2(nlopt_max_constraint_dim(m, fc),
 		    nlopt_max_constraint_dim(p, h));
      length_work(&len_w, &len_jw, mpi, pi, ni);