diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 275040cbf59..7ffa070af01 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-01-06  Martin Sebor  <msebor@redhat.com>
+
+	PR middle-end/78605
+	* gcc.dg/tree-ssa/pr78605.c: New test.
+
 2017-01-05  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/78910
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr78605.c b/gcc/testsuite/gcc.dg/tree-ssa/pr78605.c
new file mode 100644
index 00000000000..1fad3146d5b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr78605.c
@@ -0,0 +1,15 @@
+/* PR middle-end/78605 - bogus -Wformat-length=1 with %f
+   { dg-do compile }
+   { dg-options "-O2 -Wall -Wextra -Wformat-length=1" } */
+
+char d[10];
+
+int f (int i)
+{
+  return __builtin_sprintf (d, "%i %i", i, i);
+}
+
+int g (float f)
+{
+  return __builtin_sprintf (d, "%.2f %.2f", f, f);
+}