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 8731b08..275f198 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -6,6 +6,10 @@
    * Fix spurious uninitialized variable warning in cmac.c. Fix independently
      contributed by Brian J Murray and David Brown.
 
+Changes
+   * Support cmake build where Mbed TLS is a subproject. Fix
+     contributed independently by Matthieu Volat and Arne Schwabe.
+
 = mbed TLS 2.7.2 branch released 2018-03-16
 
 Security