diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d97220b5352..bec27d3d992 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2017-01-24  Martin Liska  <mliska@suse.cz>
+
+	PR bootstrap/79132
+	* tree-ssa-reassoc.c (rewrite_expr_tree_parallel): Insert assert
+	that would prevent us to call alloca with -1 as argument.
+
 2017-01-24  Jakub Jelinek  <jakub@redhat.com>
 
 	* dwarf2out.c (output_compilation_unit_header, output_file_names):
diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index 503edd3870d..4a796f48864 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -4407,6 +4407,7 @@ rewrite_expr_tree_parallel (gassign *stmt, int width,
 {
   enum tree_code opcode = gimple_assign_rhs_code (stmt);
   int op_num = ops.length ();
+  gcc_assert (op_num > 0);
   int stmt_num = op_num - 1;
   gimple **stmts = XALLOCAVEC (gimple *, stmt_num);
   int op_index = op_num - 1;