diff --git a/CMakeLists.txt b/CMakeLists.txt
index ca4cba2..2018d35 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,7 +31,7 @@
 if(PERL_FOUND)
 
     # If NULL Entropy is configured, display an appropriate warning
-    execute_process(COMMAND ${PERL_EXECUTABLE} ${CMAKE_SOURCE_DIR}/scripts/config.pl -f ${CMAKE_SOURCE_DIR}/include/mbedtls/config.h get MBEDTLS_TEST_NULL_ENTROPY
+    execute_process(COMMAND ${PERL_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/config.pl -f ${CMAKE_CURRENT_SOURCE_DIR}/include/mbedtls/config.h get MBEDTLS_TEST_NULL_ENTROPY
                         RESULT_VARIABLE result)
     if(${result} EQUAL 0)
         message(WARNING ${NULL_ENTROPY_WARNING})
diff --git a/ChangeLog b/ChangeLog
index e179989..c0759b2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -8,6 +8,8 @@
 
 Changes
    * Remove some redundant code in bignum.c. Contributed by Alexey Skalozub.
+   * Support cmake build where Mbed TLS is a subproject. Fix
+     contributed independently by Matthieu Volat and Arne Schwabe.
 
 = mbed TLS 2.8.0 branch released 2018-03-16