diff --git a/examples/dtls-sock/Makefile b/examples/dtls-sock/Makefile
index 91fa5b9907..19c63b3f63 100644
--- a/examples/dtls-sock/Makefile
+++ b/examples/dtls-sock/Makefile
@@ -61,3 +61,8 @@ ifeq (,$(filter arch_avr8,$(FEATURES_USED)))
 else
   CFLAGS += -DTHREAD_STACKSIZE_MAIN=\(4*THREAD_STACKSIZE_LARGE\)
 endif
+
+# We have two credentials for client and server, each. If we are to run both
+# server and client, we need four slots in total. The default (2) would be
+# sufficient if only client or server is ever run.
+CFLAGS += -DCONFIG_CREDMAN_MAX_CREDENTIALS=4