diff --git a/cpu/efm32/Makefile.features b/cpu/efm32/Makefile.features
index 327743ecc7..3fd4dfc3d7 100644
--- a/cpu/efm32/Makefile.features
+++ b/cpu/efm32/Makefile.features
@@ -2,6 +2,9 @@ FEATURES_PROVIDED += periph_cpuid
 FEATURES_PROVIDED += periph_flashpage
 FEATURES_PROVIDED += periph_pm
 
+FEATURES_CONFLICT += periph_rtc:periph_rtt
+FEATURES_CONFLICT_MSG += "On the EFM32, the RTC and RTT map to the same hardware peripheral."
+
 ifeq (1,$(EFM32_TNRG))
   FEATURES_PROVIDED += periph_hwrng
 endif