diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 84832c4ad..5735e4715 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -71,12 +71,13 @@ const std::string base16Chars = "0123456789abcdef";
 
 static std::string printHash16(const Hash & hash)
 {
-    char buf[hash.hashSize * 2];
+    std::string buf;
+    buf.reserve(hash.hashSize * 2);
     for (unsigned int i = 0; i < hash.hashSize; i++) {
-        buf[i * 2] = base16Chars[hash.hash[i] >> 4];
-        buf[i * 2 + 1] = base16Chars[hash.hash[i] & 0x0f];
+        buf.push_back(base16Chars[hash.hash[i] >> 4]);
+        buf.push_back(base16Chars[hash.hash[i] & 0x0f]);
     }
-    return std::string(buf, hash.hashSize * 2);
+    return buf;
 }