diff --git a/lib/tls/CMakeLists.txt b/lib/tls/CMakeLists.txt
index eaa360280..ed7a985f8 100644
--- a/lib/tls/CMakeLists.txt
+++ b/lib/tls/CMakeLists.txt
@@ -362,6 +362,7 @@ if (LWS_WITH_MBEDTLS)
 		set(LWS_HAVE_X509_VERIFY_PARAM_set1_host 1 PARENT_SCOPE)
 	endif()
 
+	set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${MBEDTLS_INCLUDE_DIRS})
 	CHECK_C_SOURCE_COMPILES("#include <mbedtls/x509_crt.h>\nint main(void) { struct mbedtls_x509_crt c; c.authority_key_id.keyIdentifier.tag = MBEDTLS_ASN1_OCTET_STRING; return c.authority_key_id.keyIdentifier.tag; }\n" LWS_HAVE_MBEDTLS_AUTH_KEY_ID)
 	CHECK_C_SOURCE_COMPILES("#include <mbedtls/ssl.h>\nint main(void) { void *v = (void *)mbedtls_ssl_set_verify; return !!v; }\n" LWS_HAVE_mbedtls_ssl_set_verify)
 	CHECK_FUNCTION_EXISTS(mbedtls_ssl_conf_alpn_protocols LWS_HAVE_mbedtls_ssl_conf_alpn_protocols PARENT_SCOPE)
diff --git a/lib/tls/mbedtls/CMakeLists.txt b/lib/tls/mbedtls/CMakeLists.txt
index adfbbbd78..e34151724 100644
--- a/lib/tls/mbedtls/CMakeLists.txt
+++ b/lib/tls/mbedtls/CMakeLists.txt
@@ -105,13 +105,16 @@ include_directories(wrapper/include wrapper/include/internal)
 	endif()
 	if (LWS_MBEDTLS_LIBRARIES)
 		set(MBEDTLS_LIBRARIES ${LWS_MBEDTLS_LIBRARIES})
+		set(MBEDTLS_LIBRARIES ${LWS_MBEDTLS_LIBRARIES} PARENT_SCOPE)
 	endif()
 	if (LWS_MBEDTLS_INCLUDE_DIRS)
 		set(MBEDTLS_INCLUDE_DIRS ${LWS_MBEDTLS_INCLUDE_DIRS})
+		set(MBEDTLS_INCLUDE_DIRS ${LWS_MBEDTLS_INCLUDE_DIRS} PARENT_SCOPE)
 	endif()
 	set(USE_MBEDTLS 1 PARENT_SCOPE)
 	if (DEFINED MBEDTLS_INCLUDE_DIRS)
 		include_directories(${MBEDTLS_INCLUDE_DIRS})
+		set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${MBEDTLS_INCLUDE_DIRS})
 	endif()
 
 	if (DEFINED MBEDTLS_LIBRARIES)