diff --git a/os/rt/include/ch.h b/os/rt/include/ch.h
index d49aa21fb..c88d39578 100644
--- a/os/rt/include/ch.h
+++ b/os/rt/include/ch.h
@@ -64,8 +64,8 @@
 
 /* Core headers.*/
 #include "chtypes.h"
-#include "chsystypes.h"
 #include "chconf.h"
+#include "chsystypes.h"
 #include "chcore.h"
 #include "chdebug.h"
 #include "chtm.h"
diff --git a/os/rt/include/chsystypes.h b/os/rt/include/chsystypes.h
index 74a45b8a2..2a64488db 100644
--- a/os/rt/include/chsystypes.h
+++ b/os/rt/include/chsystypes.h
@@ -50,8 +50,10 @@
  */
 #if (CH_CFG_ST_RESOLUTION == 32) || defined(__DOXYGEN__)
 typedef uint32_t systime_t;
-#else
+#elif CH_CFG_ST_RESOLUTION == 16
 typedef uint16_t systime_t;
+#else
+#error "invalid CH_CFG_ST_RESOLUTION setting"
 #endif
 
 /**