diff --git a/pkg/tinydtls/Makefile.dep b/pkg/tinydtls/Makefile.dep
index 151dc2636e..446cb8a9a5 100644
--- a/pkg/tinydtls/Makefile.dep
+++ b/pkg/tinydtls/Makefile.dep
@@ -6,5 +6,9 @@ USEMODULE += random
 USEMODULE += tinydtls_aes
 USEMODULE += tinydtls_ecc
 
+# tinydtls needs cryptographically secure randomness
+# TODO: restore configurability, e.g. allow to use HWRNG instead if available
+USEMODULE += prng_sha1prng
+
 # TinyDTLS only has support for 32-bit architectures ATM
 FEATURES_REQUIRED += arch_32bit