diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index c635f776e34..33f5e9f5225 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2018-07-30  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR tree-optimization/86506
+	* hwint.h (ceil_log2): Resync with hwint.c implementation.
+
 2018-07-30  Ilya Leoshkevich  <iii@linux.ibm.com>
 
         PR target/86547
diff --git a/gcc/hwint.h b/gcc/hwint.h
index 5054d8e3883..8068cad1229 100644
--- a/gcc/hwint.h
+++ b/gcc/hwint.h
@@ -242,7 +242,7 @@ floor_log2 (unsigned HOST_WIDE_INT x)
 static inline int
 ceil_log2 (unsigned HOST_WIDE_INT x)
 {
-  return floor_log2 (x - 1) + 1;
+  return x == 0 ? 0 : floor_log2 (x - 1) + 1;
 }
 
 static inline int