diff --git a/src/wg/relayconf.cpp b/src/wg/relayconf.cpp
index 362a82a..72a10dd 100644
--- a/src/wg/relayconf.cpp
+++ b/src/wg/relayconf.cpp
@@ -42,6 +42,11 @@ bool parseRelayConf(const std::string &path, RelayConf &conf, std::string &errOu
         std::string key   = trim(trimmed.substr(0, eq));
         std::string value = trim(trimmed.substr(eq + 1));
 
+        if (key.empty()) {
+            errOut = "relay.conf line " + std::to_string(lineNum) + ": missing key before '='";
+            return false;
+        }
+
         if (key == "server_address")    conf.server_address    = value;
         else if (key == "private_key")  conf.private_key       = value;
         else if (key == "server_public_key") conf.server_public_key = value;