diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 152719cc60d..426577b942b 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,7 @@
+2017-07-19  Tom de Vries  <tom@codesourcery.com>
+
+	* gimple.h (gimple_phi_set_arg): Make assert more strict.
+
 2017-07-19  Tom de Vries  <tom@codesourcery.com>
 
 	* gimple.h (gimple_phi_arg): Make assert more strict.
diff --git a/gcc/gimple.h b/gcc/gimple.h
index e19cc1c6bb3..aba7167f381 100644
--- a/gcc/gimple.h
+++ b/gcc/gimple.h
@@ -4351,7 +4351,7 @@ gimple_phi_arg (gimple *gs, unsigned index)
 static inline void
 gimple_phi_set_arg (gphi *phi, unsigned index, struct phi_arg_d * phiarg)
 {
-  gcc_gimple_checking_assert (index <= phi->nargs);
+  gcc_gimple_checking_assert (index < phi->nargs);
   phi->args[index] = *phiarg;
 }