diff --git a/src/config.h b/src/config.h
index ea206b8..ff8ae08 100644
--- a/src/config.h
+++ b/src/config.h
@@ -34,12 +34,16 @@
 #define EEPROM_MAGIC2 0x0d
 #define EEPROM_VERSION 1
 
-#define OPENWEATHERMAP_API_KEY ""
 #include "secrets.h"
 #if !defined(WIFI_SSID) || !defined(WIFI_PASS)
 #error "Please define WIFI_SSID and WIFI_PASS in secrets.h"
 #endif
 
+#if !defined(OPENWEATHERMAP_API_KEY)
+#define OPENWEATHERMAP_API_KEY "" // Put the actual key in secrets.h. NOT HERE.
+#warning "OPENWEATHERMAP_API_KEY not defined in secrets.h"
+#endif
+
 #define DEFAULT_TZ_OFFSET 3600 * 3
 
 #define NTP_SERVER "pool.ntp.org"