diff --git a/configure.ac b/configure.ac
index 098bf601..84caec35 100644
--- a/configure.ac
+++ b/configure.ac
@@ -250,6 +250,8 @@ else
         ])
 fi
 
+AC_CHECK_HEADERS([valgrind/memcheck.h])
+
 if test "$with_async" = "no" ; then
 	have_async=no
 else
diff --git a/src/libespeak-ng/compiledata.c b/src/libespeak-ng/compiledata.c
index ef95c00a..319d23b8 100644
--- a/src/libespeak-ng/compiledata.c
+++ b/src/libespeak-ng/compiledata.c
@@ -2608,7 +2608,12 @@ espeak_ng_CompilePhonemeDataPath(long rate,
 	memset(ref_hash_tab, 0, sizeof(ref_hash_tab));
 
 	n_phoneme_tabs = 0;
+	MAKE_MEM_UNDEFINED(&n_phcodes_list, sizeof(n_phcodes_list));
+	MAKE_MEM_UNDEFINED(&phoneme_tab_list2, sizeof(phoneme_tab_list2));
+
 	stack_ix = 0;
+	MAKE_MEM_UNDEFINED(&stack, sizeof(stack));
+
 	StartPhonemeTable("base");
 	CompilePhonemeFiles();
 
diff --git a/src/libespeak-ng/readclause.c b/src/libespeak-ng/readclause.c
index de6cea56..e8dbc57d 100644
--- a/src/libespeak-ng/readclause.c
+++ b/src/libespeak-ng/readclause.c
@@ -997,7 +997,9 @@ void InitText2(void)
 	ungot_char2 = 0;
 
 	n_ssml_stack = 1;
+	MAKE_MEM_UNDEFINED(&ssml_stack[1], sizeof(ssml_stack) - sizeof(ssml_stack[0]));
 	n_param_stack = 1;
+	MAKE_MEM_UNDEFINED(&param_stack[1], sizeof(param_stack) - sizeof(param_stack[0]));
 	ssml_stack[0].tag_type = 0;
 
 	for (param = 0; param < N_SPEECH_PARAM; param++)
diff --git a/src/libespeak-ng/speech.h b/src/libespeak-ng/speech.h
index 31a7aa9c..5e2433b5 100644
--- a/src/libespeak-ng/speech.h
+++ b/src/libespeak-ng/speech.h
@@ -23,6 +23,21 @@
 #include <endian.h>               // for BYTE_ORDER, BIG_ENDIAN
 #include <espeak-ng/espeak_ng.h>
 
+#if defined(__has_feature)
+#  if __has_feature(memory_sanitizer)
+#    include <sanitizer/msan_interface.h>
+#    define MAKE_MEM_UNDEFINED(addr, len) __msan_unpoison(addr, len)
+#  endif
+#endif
+
+#ifndef MAKE_MEM_UNDEFINED
+#  ifdef HAVE_VALGRIND_MEMCHECK_H
+#    include <valgrind/memcheck.h>
+#    define MAKE_MEM_UNDEFINED(addr, len) VALGRIND_MAKE_MEM_UNDEFINED(addr, len)
+#  else
+#    define MAKE_MEM_UNDEFINED(addr, len) ((void) (addr, len))
+#  endif
+#endif
 
 #ifdef __cplusplus
 extern "C"
diff --git a/src/libespeak-ng/wavegen.c b/src/libespeak-ng/wavegen.c
index 2b3ede27..9441f201 100644
--- a/src/libespeak-ng/wavegen.c
+++ b/src/libespeak-ng/wavegen.c
@@ -45,6 +45,7 @@
 #endif
 
 #include "sintab.h"
+#include "speech.h"
 
 static void SetSynth(int length, int modn, frame_t *fr1, frame_t *fr2, voice_t *v);
 
@@ -271,6 +272,7 @@ void WcmdqInc()
 
 static void WcmdqIncHead()
 {
+	MAKE_MEM_UNDEFINED(&wcmdq[wcmdq_head], sizeof(wcmdq[wcmdq_head]));
 	wcmdq_head++;
 	if (wcmdq_head >= N_WCMDQ) wcmdq_head = 0;
 }