diff --git a/pkg/mynewt-core/contrib/Makefile b/pkg/mynewt-core/contrib/Makefile
index 0bb65a903f..c16f097dad 100644
--- a/pkg/mynewt-core/contrib/Makefile
+++ b/pkg/mynewt-core/contrib/Makefile
@@ -3,7 +3,7 @@ MODULE = mynewt-core
 # exclude submodule sources from *.c wildcard source selection
 SRC := $(filter-out nrf5x_isr.c cputime.c,$(wildcard *.c))
 
-ifneq (,$(filter nrf%,$(CPU)))
+ifneq (,$(filter nrf5%,$(CPU)))
   SRC += nrf5x_isr.c
 else
   SRC += cputime.c
diff --git a/pkg/mynewt-core/mynewt-core_os.mk b/pkg/mynewt-core/mynewt-core_os.mk
index 8077bdeabe..6bfbccbb1b 100644
--- a/pkg/mynewt-core/mynewt-core_os.mk
+++ b/pkg/mynewt-core/mynewt-core_os.mk
@@ -8,7 +8,7 @@ SRC := \
   os_cputime_pwr2.c \
   #
 
-ifneq (,$(filter nrf%,$(CPU)))
+ifneq (,$(filter nrf5%,$(CPU)))
   SRC += os_cputime.c
 endif