diff --git a/CMakeLists.txt b/CMakeLists.txt
index 094d906..7ae33cc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -6,6 +6,7 @@
 
 option(ENABLE_PROGRAMS "Build mbed TLS programs." ON)
 
+option(UNSAFE_BUILD "Allow unsafe builds. These builds ARE NOT SECURE." OFF)
 
 # the test suites currently have compile errors with MSVC
 if(MSVC)
@@ -14,6 +15,35 @@
     option(ENABLE_TESTING "Build mbed TLS tests." ON)
 endif()
 
+find_package(Perl)
+if(PERL_FOUND)
+
+    # If NULL Entropy is configured, display an appropriate warning
+    execute_process(COMMAND ${PERL_EXECUTABLE} scripts/config.pl get MBEDTLS_TEST_NULL_ENTROPY
+                        RESULT_VARIABLE result)
+    if(${result} EQUAL 0)
+        message(WARNING "\
+            *******************************************************
+            ****  WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined!
+            ****  THIS BUILD HAS NO DEFINED ENTROPY SOURCES
+            ****  AND IS *NOT* SUITABLE FOR PRODUCTION USE
+            *******************************************************")
+        if(NOT UNSAFE_BUILD)
+            message(FATAL_ERROR "\
+\n\
+Warning! You have enabled MBEDTLS_TEST_NULL_ENTROPY. \
+This option is not safe for production use and negates all security \
+It is intended for development use only. \
+\n\
+To confirm you want to build with this option, re-run cmake with the \
+option: \n\
+  cmake -DUNSAFE_BUILD=ON ")
+
+            return()
+        endif()
+    endif()
+endif()
+
 set(CMAKE_BUILD_TYPE ${CMAKE_BUILD_TYPE}
     CACHE STRING "Choose the type of build: None Debug Release Coverage ASan ASanDbg MemSan MemSanDbg Check CheckFull"
     FORCE)
diff --git a/Makefile b/Makefile
index 7f03115..1283627 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@
 
 .PHONY: all no_test programs lib tests install uninstall clean test check covtest lcov apidoc apidoc_clean
 
-all: programs tests
+all: programs tests post_build
 
 no_test: programs
 
@@ -53,6 +53,20 @@
 	done
 endif
 
+WARNING_BORDER      =*******************************************************\n
+NULL_ENTROPY_WARN_L1=****  WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! ****\n
+NULL_ENTROPY_WARN_L2=****  THIS BUILD HAS NO DEFINED ENTROPY SOURCES    ****\n
+NULL_ENTROPY_WARN_L3=****  AND IS *NOT* SUITABLE FOR PRODUCTION USE     ****\n
+
+NULL_ENTROPY_WARNING=\n$(WARNING_BORDER)$(NULL_ENTROPY_WARN_L1)$(NULL_ENTROPY_WARN_L2)$(NULL_ENTROPY_WARN_L3)$(WARNING_BORDER)
+
+# Post build steps
+post_build:
+	# If NULL Entropy is configured, display an appropriate warning
+	-scripts/config.pl get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
+	    echo '$(NULL_ENTROPY_WARNING)'
+
+
 clean:
 	$(MAKE) -C library clean
 	$(MAKE) -C programs clean
diff --git a/library/entropy.c b/library/entropy.c
index 282640f..45c894b 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -28,9 +28,9 @@
 #if defined(MBEDTLS_ENTROPY_C)
 
 #if defined(MBEDTLS_TEST_NULL_ENTROPY)
-#warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! ****"
-#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES    ****"
-#warning "**** NOT SUITABLE FOR PRODUCTION                  ****"
+#warning "**** WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined! "
+#warning "**** THIS BUILD HAS NO DEFINED ENTROPY SOURCES "
+#warning "**** THIS BUILD IS *NOT* SUITABLE FOR PRODUCTION USE "
 #endif
 
 #include "mbedtls/entropy.h"