diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 67a05f83b8..c80e286baf 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -247,6 +247,9 @@
 #if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN) &&  !defined(MBEDTLS_HAS_MEMSAN)
 #error "MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN requires building with MemorySanitizer"
 #endif
+#if defined(MBEDTLS_HAS_MEMSAN) && defined(MBEDTLS_HAVE_ASM)
+#error "MemorySanitizer does not support assembly implementation"
+#endif
 #undef MBEDTLS_HAS_MEMSAN // temporary macro defined above
 
 #if defined(MBEDTLS_CCM_C) && \
diff --git a/library/constant_time_impl.h b/library/constant_time_impl.h
index 2a4574ba68..aeaeecb7de 100644
--- a/library/constant_time_impl.h
+++ b/library/constant_time_impl.h
@@ -36,24 +36,9 @@
     #pragma GCC diagnostic ignored "-Wredundant-decls"
 #endif
 
-/* Disable asm under Memsan because it confuses Memsan and generates false errors.
- *
- * We also disable under Valgrind by default, because it's more useful
- * for Valgrind to test the plain C implementation. MBEDTLS_TEST_CONSTANT_FLOW_ASM //no-check-names
- * may be set to permit building asm under Valgrind.
- */
-#if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN) || \
-    (defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND) && !defined(MBEDTLS_TEST_CONSTANT_FLOW_ASM)) //no-check-names
-#define MBEDTLS_CT_NO_ASM
-#elif defined(__has_feature)
-#if __has_feature(memory_sanitizer)
-#define MBEDTLS_CT_NO_ASM
-#endif
-#endif
-
 /* armcc5 --gnu defines __GNUC__ but doesn't support GNU's extended asm */
 #if defined(MBEDTLS_HAVE_ASM) && defined(__GNUC__) && (!defined(__ARMCC_VERSION) || \
-    __ARMCC_VERSION >= 6000000) && !defined(MBEDTLS_CT_NO_ASM)
+    __ARMCC_VERSION >= 6000000)
 #define MBEDTLS_CT_ASM
 #if (defined(__arm__) || defined(__thumb__) || defined(__thumb2__))
 #define MBEDTLS_CT_ARM_ASM
diff --git a/tests/scripts/components-sanitizers.sh b/tests/scripts/components-sanitizers.sh
index 5b79d2b778..c9648aa48d 100644
--- a/tests/scripts/components-sanitizers.sh
+++ b/tests/scripts/components-sanitizers.sh
@@ -42,6 +42,7 @@ component_test_memsan_constant_flow () {
     scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
     scripts/config.py unset MBEDTLS_USE_PSA_CRYPTO
     scripts/config.py unset MBEDTLS_AESNI_C # memsan doesn't grok asm
+    scripts/config.py unset MBEDTLS_HAVE_ASM
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=MemSan .
     make
 
@@ -60,6 +61,7 @@ component_test_memsan_constant_flow_psa () {
     scripts/config.py full
     scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN
     scripts/config.py unset MBEDTLS_AESNI_C # memsan doesn't grok asm
+    scripts/config.py unset MBEDTLS_HAVE_ASM
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=MemSan .
     make
 
@@ -93,7 +95,6 @@ component_release_test_valgrind_constant_flow () {
     # Test asm path in constant time module - by default, it will test the plain C
     # path under Valgrind or Memsan. Running only the constant_time tests is fast (<1s)
     msg "test: valgrind asm constant_time"
-    scripts/config.py --force set MBEDTLS_TEST_CONSTANT_FLOW_ASM
     skip_all_except_given_suite test_suite_constant_time
     cmake -D CMAKE_BUILD_TYPE:String=Release .
     make clean
@@ -101,6 +102,32 @@ component_release_test_valgrind_constant_flow () {
     make memcheck
 }
 
+component_release_test_valgrind_constant_flow_no_asm () {
+    # This tests both (1) everything that valgrind's memcheck usually checks
+    # (heap buffer overflows, use of uninitialized memory, use-after-free,
+    # etc.) and (2) branches or memory access depending on secret values,
+    # which will be reported as uninitialized memory. To distinguish between
+    # secret and actually uninitialized:
+    # - unset MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND - does the failure persist?
+    # - or alternatively, build with debug info and manually run the offending
+    # test suite with valgrind --track-origins=yes, then check if the origin
+    # was TEST_CF_SECRET() or something else.
+    msg "build: cmake release GCC, full config minus MBEDTLS_USE_PSA_CRYPTO, minus MBEDTLS_HAVE_ASM with constant flow testing"
+    scripts/config.py full
+    scripts/config.py set MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND
+    scripts/config.py unset MBEDTLS_USE_PSA_CRYPTO
+    scripts/config.py unset MBEDTLS_AESNI_C
+    scripts/config.py unset MBEDTLS_HAVE_ASM
+    skip_suites_without_constant_flow
+    cmake -D CMAKE_BUILD_TYPE:String=Release .
+    make
+
+    # this only shows a summary of the results (how many of each type)
+    # details are left in Testing/<date>/DynamicAnalysis.xml
+    msg "test: some suites (full minus MBEDTLS_USE_PSA_CRYPTO, minus MBEDTLS_HAVE_ASM, valgrind + constant flow)"
+    make memcheck
+}
+
 component_release_test_valgrind_constant_flow_psa () {
     # This tests both (1) everything that valgrind's memcheck usually checks
     # (heap buffer overflows, use of uninitialized memory, use-after-free,
@@ -145,6 +172,7 @@ component_test_tsan () {
 component_test_memsan () {
     msg "build: MSan (clang)" # ~ 1 min 20s
     scripts/config.py unset MBEDTLS_AESNI_C # memsan doesn't grok asm
+    scripts/config.py unset MBEDTLS_HAVE_ASM
     CC=clang cmake -D CMAKE_BUILD_TYPE:String=MemSan .
     make