diff --git a/tests/periph_rtt/Makefile b/tests/periph_rtt/Makefile
index 80c2d54209..08887559e5 100644
--- a/tests/periph_rtt/Makefile
+++ b/tests/periph_rtt/Makefile
@@ -8,9 +8,11 @@ DISABLE_MODULE += periph_init_rtt
 include $(RIOTBASE)/Makefile.include
 
 # Put board specific dependencies here
-ifneq (,$(filter-out stm32f1,$(filter stm32%,$(CPU))))
-  # all stm32% but stm32f1 RTT are based on a 16 bit LPTIM, if using the default
-  # 32768KHz configuration TICKS_TO_WAIT will overflow
-  RTT_FREQUENCY ?= 1024
-  CFLAGS += -DRTT_FREQUENCY=$(RTT_FREQUENCY)
+ifeq (stm32,$(CPU))
+  ifneq (f1,$(CPU_FAM))
+    # all stm32% but stm32f1 RTT are based on a 16 bit LPTIM, if using the default
+    # 32768KHz configuration TICKS_TO_WAIT will overflow
+    RTT_FREQUENCY ?= 1024
+    CFLAGS += -DRTT_FREQUENCY=$(RTT_FREQUENCY)
+  endif
 endif