diff --git a/CMakeLists.txt b/CMakeLists.txt
index fb1ffaf..f648f22 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -56,17 +56,6 @@
 endif()
 
 # Warning string - created as a list for compatibility with CMake 2.8
-set(WARNING_BORDER "*******************************************************\n")
-set(NULL_ENTROPY_WARN_L1 "****  WARNING!  MBEDTLS_TEST_NULL_ENTROPY defined!\n")
-set(NULL_ENTROPY_WARN_L2 "****  THIS BUILD HAS NO DEFINED ENTROPY SOURCES\n")
-set(NULL_ENTROPY_WARN_L3 "****  AND IS *NOT* SUITABLE FOR PRODUCTION USE\n")
-
-set(NULL_ENTROPY_WARNING "${WARNING_BORDER}"
-                         "${NULL_ENTROPY_WARN_L1}"
-                         "${NULL_ENTROPY_WARN_L2}"
-                         "${NULL_ENTROPY_WARN_L3}"
-                         "${WARNING_BORDER}")
-
 set(CTR_DRBG_128_BIT_KEY_WARN_L1 "****  WARNING!  MBEDTLS_CTR_DRBG_USE_128_BIT_KEY defined!\n")
 set(CTR_DRBG_128_BIT_KEY_WARN_L2 "****  Using 128-bit keys for CTR_DRBG limits the security of generated\n")
 set(CTR_DRBG_128_BIT_KEY_WARN_L3 "****  keys and operations that use random values generated to 128-bit security\n")
@@ -99,26 +88,6 @@
         message(WARNING ${CTR_DRBG_128_BIT_KEY_WARNING})
     endif()
 
-    # If NULL Entropy is configured, display an appropriate warning
-    execute_process(COMMAND ${MBEDTLS_PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/scripts/config.py -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})
-
-        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()
 
 # If this is the root project add longer list of available CMAKE_BUILD_TYPE values
diff --git a/ChangeLog.d/remove_null_entropy.txt b/ChangeLog.d/remove_null_entropy.txt
new file mode 100644
index 0000000..3d9674b
--- /dev/null
+++ b/ChangeLog.d/remove_null_entropy.txt
@@ -0,0 +1,2 @@
+API changes
+   * Remove the MBEDTLS_TEST_NULL_ENTROPY config option. Fixes #4388.
diff --git a/Makefile b/Makefile
index 6a8b230..8d1a6ce 100644
--- a/Makefile
+++ b/Makefile
@@ -59,12 +59,6 @@
 	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)
 
 WARNING_BORDER_LONG      =**********************************************************************************\n
 CTR_DRBG_128_BIT_KEY_WARN_L1=****  WARNING!  MBEDTLS_CTR_DRBG_USE_128_BIT_KEY defined!                      ****\n
@@ -81,9 +75,6 @@
 	-scripts/config.py get MBEDTLS_CTR_DRBG_USE_128_BIT_KEY && ([ $$? -eq 0 ]) && \
 	    echo '$(CTR_DRBG_128_BIT_KEY_WARNING)'
 
-	# If NULL Entropy is configured, display an appropriate warning
-	-scripts/config.py get MBEDTLS_TEST_NULL_ENTROPY && ([ $$? -eq 0 ]) && \
-	    echo '$(NULL_ENTROPY_WARNING)'
 endif
 
 clean:
diff --git a/docs/3.0-migration-guide.d/remove-null-entropy.md b/docs/3.0-migration-guide.d/remove-null-entropy.md
new file mode 100644
index 0000000..50e024a
--- /dev/null
+++ b/docs/3.0-migration-guide.d/remove-null-entropy.md
@@ -0,0 +1,11 @@
+Remove the option to build the library without any entropy sources
+------------------------------------------------------------------
+
+This does not affect users who use the default `config.h`, as this option was
+already off by default.
+
+If you were using the `MBEDTLS_TEST_NULL_ENTROPY` option and your platform
+doesn't have any entropy source, you should use `MBEDTLS_ENTROPY_NV_SEED`
+and make sure your device is provisioned with a strong random seed.
+Alternatively, for testing purposes only, you can create and register a fake
+entropy function.
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 47b5de0..4a2d70f 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -201,15 +201,6 @@
 #endif
 #undef MBEDTLS_HAS_MEMSAN
 
-#if defined(MBEDTLS_TEST_NULL_ENTROPY) && \
-    ( !defined(MBEDTLS_ENTROPY_C) || !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES) )
-#error "MBEDTLS_TEST_NULL_ENTROPY defined, but not all prerequisites"
-#endif
-#if defined(MBEDTLS_TEST_NULL_ENTROPY) && \
-     ( defined(MBEDTLS_ENTROPY_NV_SEED) || defined(MBEDTLS_ENTROPY_HARDWARE_ALT) )
-#error "MBEDTLS_TEST_NULL_ENTROPY defined, but entropy sources too"
-#endif
-
 #if defined(MBEDTLS_GCM_C) && (                                        \
         !defined(MBEDTLS_AES_C) && !defined(MBEDTLS_CAMELLIA_C) && !defined(MBEDTLS_ARIA_C) )
 #error "MBEDTLS_GCM_C defined, but not all prerequisites"
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index 8e94599..bc39a12 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -528,23 +528,6 @@
 //#define MBEDTLS_ECP_NORMALIZE_MXZ_ALT
 
 /**
- * \def MBEDTLS_TEST_NULL_ENTROPY
- *
- * Enables testing and use of mbed TLS without any configured entropy sources.
- * This permits use of the library on platforms before an entropy source has
- * been integrated (see for example the MBEDTLS_ENTROPY_HARDWARE_ALT or the
- * MBEDTLS_ENTROPY_NV_SEED switches).
- *
- * WARNING! This switch MUST be disabled in production builds, and is suitable
- * only for development.
- * Enabling the switch negates any security provided by the library.
- *
- * Requires MBEDTLS_ENTROPY_C, MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
- *
- */
-//#define MBEDTLS_TEST_NULL_ENTROPY
-
-/**
  * \def MBEDTLS_ENTROPY_HARDWARE_ALT
  *
  * Uncomment this macro to let mbed TLS use your own implementation of a
diff --git a/library/entropy.c b/library/entropy.c
index c7ae97a..cc68628 100644
--- a/library/entropy.c
+++ b/library/entropy.c
@@ -21,12 +21,6 @@
 
 #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 "**** THIS BUILD IS *NOT* SUITABLE FOR PRODUCTION USE "
-#endif
-
 #include "mbedtls/entropy.h"
 #include "entropy_poll.h"
 #include "mbedtls/platform_util.h"
@@ -73,11 +67,6 @@
     /* Reminder: Update ENTROPY_HAVE_STRONG in the test files
      *           when adding more strong entropy sources here. */
 
-#if defined(MBEDTLS_TEST_NULL_ENTROPY)
-    mbedtls_entropy_add_source( ctx, mbedtls_null_entropy_poll, NULL,
-                                1, MBEDTLS_ENTROPY_SOURCE_STRONG );
-#endif
-
 #if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES)
 #if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
     mbedtls_entropy_add_source( ctx, mbedtls_platform_entropy_poll, NULL,
@@ -524,7 +513,6 @@
 #endif /* MBEDTLS_FS_IO */
 
 #if defined(MBEDTLS_SELF_TEST)
-#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
 /*
  * Dummy source function
  */
@@ -538,7 +526,6 @@
 
     return( 0 );
 }
-#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
 
 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
 
@@ -646,17 +633,14 @@
 int mbedtls_entropy_self_test( int verbose )
 {
     int ret = 1;
-#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_context ctx;
     unsigned char buf[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
     unsigned char acc[MBEDTLS_ENTROPY_BLOCK_SIZE] = { 0 };
     size_t i, j;
-#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
 
     if( verbose != 0 )
         mbedtls_printf( "  ENTROPY test: " );
 
-#if !defined(MBEDTLS_TEST_NULL_ENTROPY)
     mbedtls_entropy_init( &ctx );
 
     /* First do a gather to make sure we have default sources */
@@ -704,7 +688,6 @@
 
 cleanup:
     mbedtls_entropy_free( &ctx );
-#endif /* !MBEDTLS_TEST_NULL_ENTROPY */
 
     if( verbose != 0 )
     {
diff --git a/library/entropy_poll.c b/library/entropy_poll.c
index e4ffe2b..e5d75c5 100644
--- a/library/entropy_poll.c
+++ b/library/entropy_poll.c
@@ -211,23 +211,6 @@
 #endif /* _WIN32 && !EFIX64 && !EFI32 */
 #endif /* !MBEDTLS_NO_PLATFORM_ENTROPY */
 
-#if defined(MBEDTLS_TEST_NULL_ENTROPY)
-int mbedtls_null_entropy_poll( void *data,
-                    unsigned char *output, size_t len, size_t *olen )
-{
-    ((void) data);
-    ((void) output);
-
-    *olen = 0;
-    if( len < sizeof(unsigned char) )
-        return( 0 );
-
-    output[0] = 0;
-    *olen = sizeof(unsigned char);
-    return( 0 );
-}
-#endif
-
 #if defined(MBEDTLS_TIMING_C)
 int mbedtls_hardclock_poll( void *data,
                     unsigned char *output, size_t len, size_t *olen )
diff --git a/library/entropy_poll.h b/library/entropy_poll.h
index e12a134..9120fe5 100644
--- a/library/entropy_poll.h
+++ b/library/entropy_poll.h
@@ -43,14 +43,6 @@
 #define MBEDTLS_ENTROPY_MIN_HARDWARE     32     /**< Minimum for the hardware source */
 #endif
 
-/**
- * \brief           Entropy poll callback that provides 0 entropy.
- */
-#if defined(MBEDTLS_TEST_NULL_ENTROPY)
-    int mbedtls_null_entropy_poll( void *data,
-                                unsigned char *output, size_t len, size_t *olen );
-#endif
-
 #if !defined(MBEDTLS_NO_PLATFORM_ENTROPY)
 /**
  * \brief           Platform-specific entropy poll callback
diff --git a/library/version_features.c b/library/version_features.c
index b42fb29..b2b6336 100644
--- a/library/version_features.c
+++ b/library/version_features.c
@@ -252,9 +252,6 @@
 #if defined(MBEDTLS_ECP_NORMALIZE_MXZ_ALT)
     "MBEDTLS_ECP_NORMALIZE_MXZ_ALT",
 #endif /* MBEDTLS_ECP_NORMALIZE_MXZ_ALT */
-#if defined(MBEDTLS_TEST_NULL_ENTROPY)
-    "MBEDTLS_TEST_NULL_ENTROPY",
-#endif /* MBEDTLS_TEST_NULL_ENTROPY */
 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
     "MBEDTLS_ENTROPY_HARDWARE_ALT",
 #endif /* MBEDTLS_ENTROPY_HARDWARE_ALT */
diff --git a/programs/test/query_config.c b/programs/test/query_config.c
index 79c2c54..25c334c 100644
--- a/programs/test/query_config.c
+++ b/programs/test/query_config.c
@@ -723,14 +723,6 @@
     }
 #endif /* MBEDTLS_ECP_NORMALIZE_MXZ_ALT */
 
-#if defined(MBEDTLS_TEST_NULL_ENTROPY)
-    if( strcmp( "MBEDTLS_TEST_NULL_ENTROPY", config ) == 0 )
-    {
-        MACRO_EXPANSION_TO_STR( MBEDTLS_TEST_NULL_ENTROPY );
-        return( 0 );
-    }
-#endif /* MBEDTLS_TEST_NULL_ENTROPY */
-
 #if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
     if( strcmp( "MBEDTLS_ENTROPY_HARDWARE_ALT", config ) == 0 )
     {
diff --git a/scripts/config.py b/scripts/config.py
index a77ead0..a68b2a9 100755
--- a/scripts/config.py
+++ b/scripts/config.py
@@ -194,7 +194,6 @@
     'MBEDTLS_SHA512_NO_SHA384', # removes a feature
     'MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN', # build dependency (clang+memsan)
     'MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND', # build dependency (valgrind headers)
-    'MBEDTLS_TEST_NULL_ENTROPY', # removes a feature
     'MBEDTLS_X509_ALLOW_UNSUPPORTED_CRITICAL_EXTENSION', # influences the use of X.509 in TLS
     'MBEDTLS_X509_REMOVE_INFO', # removes a feature
 ])
diff --git a/tests/scripts/all.sh b/tests/scripts/all.sh
index 8b9d7d1..350f6f9 100755
--- a/tests/scripts/all.sh
+++ b/tests/scripts/all.sh
@@ -2074,21 +2074,6 @@
     if_build_succeeded tests/ssl-opt.sh -f 'Default\|EtM' -e 'without EtM'
 }
 
-component_test_null_entropy () {
-    msg "build: default config with  MBEDTLS_TEST_NULL_ENTROPY (ASan build)"
-    scripts/config.py set MBEDTLS_TEST_NULL_ENTROPY
-    scripts/config.py set MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES
-    scripts/config.py set MBEDTLS_ENTROPY_C
-    scripts/config.py unset MBEDTLS_ENTROPY_NV_SEED
-    scripts/config.py unset MBEDTLS_PLATFORM_NV_SEED_ALT
-    scripts/config.py unset MBEDTLS_ENTROPY_HARDWARE_ALT
-    CC=gcc cmake -D CMAKE_BUILD_TYPE:String=Asan -D UNSAFE_BUILD=ON .
-    make
-
-    msg "test: MBEDTLS_TEST_NULL_ENTROPY - main suites (inc. selftests) (ASan build)"
-    make test
-}
-
 component_test_no_date_time () {
     msg "build: default config without MBEDTLS_HAVE_TIME_DATE"
     scripts/config.py unset MBEDTLS_HAVE_TIME_DATE
diff --git a/tests/suites/helpers.function b/tests/suites/helpers.function
index 27d9249..2ef07fa 100644
--- a/tests/suites/helpers.function
+++ b/tests/suites/helpers.function
@@ -87,11 +87,10 @@
 
 /* Indicates whether we expect mbedtls_entropy_init
  * to initialize some strong entropy source. */
-#if defined(MBEDTLS_TEST_NULL_ENTROPY) ||             \
-    ( !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES) && \
-      ( !defined(MBEDTLS_NO_PLATFORM_ENTROPY)  ||     \
-         defined(MBEDTLS_ENTROPY_HARDWARE_ALT) ||     \
-         defined(ENTROPY_NV_SEED) ) )
+#if !defined(MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES) && \
+    ( !defined(MBEDTLS_NO_PLATFORM_ENTROPY) ||      \
+        defined(MBEDTLS_ENTROPY_HARDWARE_ALT) ||    \
+        defined(ENTROPY_NV_SEED) )
 #define ENTROPY_HAVE_STRONG
 #endif
 
diff --git a/tests/suites/test_suite_entropy.data b/tests/suites/test_suite_entropy.data
index 95bfe66..0b30bb8 100644
--- a/tests/suites/test_suite_entropy.data
+++ b/tests/suites/test_suite_entropy.data
@@ -83,9 +83,4 @@
 entropy_nv_seed:"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"
 
 Entropy self test
-depends_on:!MBEDTLS_TEST_NULL_ENTROPY
 entropy_selftest:0
-
-Entropy self test (MBEDTLS_TEST_NULL_ENTROPY)
-depends_on:MBEDTLS_TEST_NULL_ENTROPY
-entropy_selftest:1
diff --git a/tests/suites/test_suite_random.function b/tests/suites/test_suite_random.function
index 37fa36e..c532c8a 100644
--- a/tests/suites/test_suite_random.function
+++ b/tests/suites/test_suite_random.function
@@ -18,7 +18,7 @@
 
 /* END_HEADER */
 
-/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:!MBEDTLS_TEST_NULL_ENTROPY:MBEDTLS_CTR_DRBG_C */
+/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:MBEDTLS_CTR_DRBG_C */
 void random_twice_with_ctr_drbg( )
 {
     mbedtls_entropy_context entropy;
@@ -57,7 +57,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:!MBEDTLS_TEST_NULL_ENTROPY:MBEDTLS_HMAC_DRBG_C */
+/* BEGIN_CASE depends_on:MBEDTLS_ENTROPY_C:MBEDTLS_HMAC_DRBG_C */
 void random_twice_with_hmac_drbg( int md_type )
 {
     mbedtls_entropy_context entropy;
@@ -97,7 +97,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_TEST_NULL_ENTROPY:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
+/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 void random_twice_with_psa_from_classic( )
 {
     unsigned char output1[OUTPUT_SIZE];
@@ -123,7 +123,7 @@
 }
 /* END_CASE */
 
-/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_TEST_NULL_ENTROPY:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
+/* BEGIN_CASE depends_on:MBEDTLS_PSA_CRYPTO_C:!MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG */
 void random_twice_with_psa_from_psa( )
 {
     unsigned char output1[OUTPUT_SIZE];