diff --git a/samples/net/openthread/ncp/prj.conf b/samples/net/openthread/ncp/prj.conf
index 6707cc00fd6..ab92a25d7e6 100644
--- a/samples/net/openthread/ncp/prj.conf
+++ b/samples/net/openthread/ncp/prj.conf
@@ -13,6 +13,7 @@ CONFIG_NET_IPV6_NBR_CACHE=n
 CONFIG_NET_IPV6_MLD=n
 
 # Kernel options
+CONFIG_NEWLIB_LIBC=y
 CONFIG_MAIN_STACK_SIZE=4096
 CONFIG_ENTROPY_GENERATOR=y
 CONFIG_TEST_RANDOM_GENERATOR=y
diff --git a/samples/net/sockets/echo_client/overlay-ot.conf b/samples/net/sockets/echo_client/overlay-ot.conf
index 04c1d84024c..1d7fca47342 100644
--- a/samples/net/sockets/echo_client/overlay-ot.conf
+++ b/samples/net/sockets/echo_client/overlay-ot.conf
@@ -1,3 +1,4 @@
+CONFIG_NEWLIB_LIBC=y
 CONFIG_CPLUSPLUS=y
 
 CONFIG_BT=n
diff --git a/samples/net/sockets/echo_server/overlay-ot.conf b/samples/net/sockets/echo_server/overlay-ot.conf
index c4829e58ae5..ba6a6004848 100644
--- a/samples/net/sockets/echo_server/overlay-ot.conf
+++ b/samples/net/sockets/echo_server/overlay-ot.conf
@@ -1,3 +1,4 @@
+CONFIG_NEWLIB_LIBC=y
 CONFIG_CPLUSPLUS=y
 
 CONFIG_BT=n