diff --git a/src/libutil/url.cc b/src/libutil/url.cc
index bcbe9ea4e..78c832440 100644
--- a/src/libutil/url.cc
+++ b/src/libutil/url.cc
@@ -79,10 +79,15 @@ std::map<std::string, std::string> decodeQuery(const std::string & query)
 
     for (auto s : tokenizeString<Strings>(query, "&")) {
         auto e = s.find('=');
-        if (e != std::string::npos)
-            result.emplace(
-                s.substr(0, e),
-                percentDecode(std::string_view(s).substr(e + 1)));
+
+        if (e == std::string::npos) {
+            warn("invalid URI query '%s', did you forget an equals sign `=`?", s);
+            continue;
+        }
+
+        result.emplace(
+            s.substr(0, e),
+            percentDecode(std::string_view(s).substr(e + 1)));
     }
 
     return result;