diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a20554eff62..d84106361c3 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-05-18  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR bootstrap/85838
+	* config/sparc/sparc.c (sparc_expand_builtin): Always initialize op[0].
+
 2018-05-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	* config/arm/arm-cpus.in (armv3m, mode32): Delete features.
diff --git a/gcc/config/sparc/sparc.c b/gcc/config/sparc/sparc.c
index 4026d4933d8..768ee2b829c 100644
--- a/gcc/config/sparc/sparc.c
+++ b/gcc/config/sparc/sparc.c
@@ -11592,6 +11592,8 @@ sparc_expand_builtin (tree exp, rtx target,
       else
 	op[0] = target;
     }
+  else
+    op[0] = NULL_RTX;
 
   FOR_EACH_CALL_EXPR_ARG (arg, iter, exp)
     {