diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 64326df830a..d2342b12b69 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-01-04  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* fold-const.c (fold_ternary_loc): Check tree_fits_uhwi_p before
+	using tree_to_uhwi.
+
 2018-01-04  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	* tree-ssa-forwprop.c (is_combined_permutation_identity): Allow
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 46490cad0bc..521c2dc09ce 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -11643,7 +11643,9 @@ fold_ternary_loc (location_t loc, enum tree_code code, tree type,
       if (TREE_CODE (arg0) == VECTOR_CST
 	  && (type == TREE_TYPE (TREE_TYPE (arg0))
 	      || (TREE_CODE (type) == VECTOR_TYPE
-		  && TREE_TYPE (type) == TREE_TYPE (TREE_TYPE (arg0)))))
+		  && TREE_TYPE (type) == TREE_TYPE (TREE_TYPE (arg0))))
+	  && tree_fits_uhwi_p (op1)
+	  && tree_fits_uhwi_p (op2))
 	{
 	  tree eltype = TREE_TYPE (TREE_TYPE (arg0));
 	  unsigned HOST_WIDE_INT width = tree_to_uhwi (TYPE_SIZE (eltype));