diff --git a/src/libespeak-ng/compiledict.c b/src/libespeak-ng/compiledict.c
index 4068265e..2a472f49 100644
--- a/src/libespeak-ng/compiledict.c
+++ b/src/libespeak-ng/compiledict.c
@@ -22,6 +22,7 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/src/libespeak-ng/error.h b/src/libespeak-ng/error.h
index 7e0dcc9a..103ba619 100644
--- a/src/libespeak-ng/error.h
+++ b/src/libespeak-ng/error.h
@@ -18,6 +18,8 @@
 #ifndef ESPEAK_NG_ERROR_API
 #define ESPEAK_NG_ERROR_API
 
+#include <espeak-ng/espeak_ng.h>
+
 #ifdef __cplusplus
 extern "C"
 {
diff --git a/src/libespeak-ng/espeak_command.h b/src/libespeak-ng/espeak_command.h
index 8d1d4d23..78204d2a 100644
--- a/src/libespeak-ng/espeak_command.h
+++ b/src/libespeak-ng/espeak_command.h
@@ -16,8 +16,10 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
-#ifndef ESPEAK_COMMAND_H
-#define ESPEAK_COMMAND_H
+#ifndef ESPEAK_NG_COMMAND_H
+#define ESPEAK_NG_COMMAND_H
+
+#include <espeak-ng/espeak_ng.h>
 
 #ifdef __cplusplus
 extern "C"
diff --git a/src/libespeak-ng/event.h b/src/libespeak-ng/event.h
index abc263b2..5f47e108 100644
--- a/src/libespeak-ng/event.h
+++ b/src/libespeak-ng/event.h
@@ -16,9 +16,6 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
-#ifndef EVENT_H
-#define EVENT_H
-
 /*
    Manage events (sentence, word, mark, end,...), is responsible of calling the external
    callback as soon as the relevant audio sample is played.
@@ -39,6 +36,11 @@
 
  */
 
+#ifndef ESPEAK_NG_EVENT_H
+#define ESPEAK_NG_EVENT_H
+
+#include <espeak-ng/espeak_ng.h>
+
 #ifdef __cplusplus
 extern "C"
 {
diff --git a/src/libespeak-ng/fifo.h b/src/libespeak-ng/fifo.h
index 7d5c001e..ba5e5526 100644
--- a/src/libespeak-ng/fifo.h
+++ b/src/libespeak-ng/fifo.h
@@ -16,12 +16,15 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
-#ifndef FIFO_H
-#define FIFO_H
-
 // Helps to add espeak commands in a first-in first-out queue
 // and run them asynchronously.
 
+#ifndef ESPEAK_NG_FIFO_H
+#define ESPEAK_NG_FIFO_H
+
+#include <espeak-ng/espeak_ng.h>
+#include "espeak_command.h"
+
 #ifdef __cplusplus
 extern "C"
 {
diff --git a/src/libespeak-ng/ieee80.h b/src/libespeak-ng/ieee80.h
index 04ca67f4..df4da90f 100644
--- a/src/libespeak-ng/ieee80.h
+++ b/src/libespeak-ng/ieee80.h
@@ -42,6 +42,7 @@
  * conversions, and accommodated conversions involving +/- infinity,
  * NaN's, and denormalized numbers.
  */
+
 #ifndef IEEE_H
 #define IEEE_H
 
diff --git a/src/libespeak-ng/klatt.h b/src/libespeak-ng/klatt.h
index 23934ad5..fe2625c8 100644
--- a/src/libespeak-ng/klatt.h
+++ b/src/libespeak-ng/klatt.h
@@ -21,6 +21,12 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_KLATT_H
+#define ESPEAK_NG_KLATT_H
+
+#include "speech.h"
+#include "synthesize.h"
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -179,3 +185,5 @@ int Wavegen_Klatt2(int length, int resume, frame_t *fr1, frame_t *fr2);
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/phoneme.h b/src/libespeak-ng/phoneme.h
index 0f18ef80..fd070763 100644
--- a/src/libespeak-ng/phoneme.h
+++ b/src/libespeak-ng/phoneme.h
@@ -17,6 +17,11 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_PHONEME_H
+#define ESPEAK_NG_PHONEME_H
+
+#include <espeak-ng/espeak_ng.h>
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -291,3 +296,5 @@ extern int phoneme_tab_number;
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/sintab.h b/src/libespeak-ng/sintab.h
index 4a84d12d..628a81d3 100644
--- a/src/libespeak-ng/sintab.h
+++ b/src/libespeak-ng/sintab.h
@@ -17,6 +17,9 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_SINTAB_H
+#define ESPEAK_NG_SINTAB_H
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -284,3 +287,5 @@ short int sin_tab[2048] = {
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/spect.h b/src/libespeak-ng/spect.h
index f4f1c883..398f01cf 100644
--- a/src/libespeak-ng/spect.h
+++ b/src/libespeak-ng/spect.h
@@ -17,6 +17,13 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_SPECT_H
+#define ESPEAK_NG_SPECT_H
+
+#include <espeak-ng/espeak_ng.h>
+#include "synthesize.h"
+#include "speech.h"
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -133,3 +140,5 @@ espeak_ng_STATUS LoadSpectSeq(SpectSeq *spect, const char *filename);
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/speech.h b/src/libespeak-ng/speech.h
index 6f703b87..36159e7c 100644
--- a/src/libespeak-ng/speech.h
+++ b/src/libespeak-ng/speech.h
@@ -17,8 +17,10 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
-#ifndef SPEECH_H
-#define SPEECH_H
+#ifndef ESPEAK_NG_SPEECH_H
+#define ESPEAK_NG_SPEECH_H
+
+#include <espeak-ng/espeak_ng.h>
 
 #ifdef __cplusplus
 extern "C"
diff --git a/src/libespeak-ng/ssml.h b/src/libespeak-ng/ssml.h
index 5399542a..f47f213c 100644
--- a/src/libespeak-ng/ssml.h
+++ b/src/libespeak-ng/ssml.h
@@ -21,6 +21,11 @@
 #ifndef ESPEAK_NG_SSML_API
 #define ESPEAK_NG_SSML_API
 
+#include <stdbool.h>
+#include <wchar.h>
+
+#include <espeak-ng/speak_lib.h>
+
 #ifdef __cplusplus
 extern "C"
 {
diff --git a/src/libespeak-ng/synthesize.h b/src/libespeak-ng/synthesize.h
index 826b237f..731c1a26 100644
--- a/src/libespeak-ng/synthesize.h
+++ b/src/libespeak-ng/synthesize.h
@@ -17,13 +17,22 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
-#include <stdbool.h>
+#ifndef ESPEAK_NG_SYNTHESIZE_H
+#define ESPEAK_NG_SYNTHESIZE_H
+
+#include "speech.h"
 
 #ifdef __cplusplus
 extern "C"
 {
 #endif
 
+#include <stdint.h>
+#include <stdbool.h>
+#include <espeak-ng/espeak_ng.h>
+#include "phoneme.h"
+#include "voice.h"
+
 #define espeakINITIALIZE_PHONEME_IPA 0x0002 // move this to speak_lib.h, after eSpeak version 1.46.02
 
 #define N_PHONEME_LIST 1000 // enough for source[N_TR_SOURCE] full of text, else it will truncate
@@ -559,3 +568,5 @@ void InitBreath(void);
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/translate.h b/src/libespeak-ng/translate.h
index 2016b2d5..b9dd5af7 100644
--- a/src/libespeak-ng/translate.h
+++ b/src/libespeak-ng/translate.h
@@ -17,6 +17,16 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_TRANSLATE_H
+#define ESPEAK_NG_TRANSLATE_H
+
+#include <stdbool.h>
+
+#include <espeak-ng/espeak_ng.h>
+#include <espeak-ng/encoding.h>
+
+#include "synthesize.h"
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -784,3 +794,5 @@ extern FILE *f_trans; // for logging
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/voice.h b/src/libespeak-ng/voice.h
index ff7d7a79..8be96d8a 100644
--- a/src/libespeak-ng/voice.h
+++ b/src/libespeak-ng/voice.h
@@ -17,6 +17,13 @@
  * along with this program; if not, see: <http://www.gnu.org/licenses/>.
  */
 
+#ifndef ESPEAK_NG_VOICE_H
+#define ESPEAK_NG_VOICE_H
+
+#include <espeak-ng/espeak_ng.h>
+
+#include "speech.h"
+
 #ifdef __cplusplus
 extern "C"
 {
@@ -93,3 +100,5 @@ void FreeVoiceList(void);
 #ifdef __cplusplus
 }
 #endif
+
+#endif
diff --git a/src/libespeak-ng/wavegen.c b/src/libespeak-ng/wavegen.c
index 027a8d22..68f8a0f6 100644
--- a/src/libespeak-ng/wavegen.c
+++ b/src/libespeak-ng/wavegen.c
@@ -32,10 +32,10 @@
 #include <espeak-ng/espeak_ng.h>
 #include <espeak-ng/speak_lib.h>
 
+#include "synthesize.h"
 #include "speech.h"
 #include "phoneme.h"
 #include "voice.h"
-#include "synthesize.h"
 
 #ifdef INCLUDE_KLATT
 #include "klatt.h"