diff --git a/src/espeak-ng.c b/src/espeak-ng.c
index 1634cc1d..0891a24f 100644
--- a/src/espeak-ng.c
+++ b/src/espeak-ng.c
@@ -143,7 +143,7 @@ static void DisplayVoices(FILE *f_out, char *language)
 	const espeak_VOICE **voices;
 	espeak_VOICE voice_select;
 
-	static char genders[4] = { '-', 'M', 'F', '-' };
+	static const char genders[4] = { '-', 'M', 'F', '-' };
 
 	if ((language != NULL) && (language[0] != 0)) {
 		// display only voices for the specified language, in order of priority
@@ -201,7 +201,7 @@ static void Write4Bytes(FILE *f, int value)
 
 static int OpenWavFile(char *path, int rate)
 {
-	static unsigned char wave_hdr[44] = {
+	static const unsigned char wave_hdr[44] = {
 		'R', 'I', 'F', 'F', 0x24, 0xf0, 0xff, 0x7f, 'W', 'A', 'V', 'E', 'f', 'm', 't', ' ',
 		0x10, 0, 0, 0, 1, 0, 1, 0,  9, 0x3d, 0, 0, 0x12, 0x7a, 0, 0,
 		2, 0, 0x10, 0, 'd', 'a', 't', 'a',  0x00, 0xf0, 0xff, 0x7f
@@ -304,7 +304,7 @@ static void PrintVersion()
 
 int main(int argc, char **argv)
 {
-	static struct option long_options[] = {
+	static const struct option long_options[] = {
 		{ "help",    no_argument,       0, 'h' },
 		{ "stdin",   no_argument,       0, 0x100 },
 		{ "compile-debug", optional_argument, 0, 0x101 },
diff --git a/src/libespeak-ng/compiledata.c b/src/libespeak-ng/compiledata.c
index 319d23b8..772f10e1 100644
--- a/src/libespeak-ng/compiledata.c
+++ b/src/libespeak-ng/compiledata.c
@@ -1559,7 +1559,7 @@ static void CompileSound(int keyword, int isvowel)
 	int addr = 0;
 	int value = 0;
 	char path[N_ITEM_STRING];
-	static int sound_instns[] = { i_FMT, i_WAV, i_VWLSTART, i_VWLENDING, i_WAVADD };
+	static const int sound_instns[] = { i_FMT, i_WAV, i_VWLSTART, i_VWLENDING, i_WAVADD };
 
 	NextItemBrackets(tSTRING, 2);
 	strcpy(path, item_string);
diff --git a/src/libespeak-ng/compiledict.c b/src/libespeak-ng/compiledict.c
index 26ece6fe..6e12d571 100644
--- a/src/libespeak-ng/compiledict.c
+++ b/src/libespeak-ng/compiledict.c
@@ -223,14 +223,14 @@ char *DecodeRule(const char *group_chars, int group_length, char *rule, int cont
 	char suffix[20];
 	static char output[80];
 
-	static char symbols[] = {
+	static const char symbols[] = {
 		' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
 		'&', '%', '+', '#', 'S', 'D', 'Z', 'A', 'L', '!',
 		' ', '@', '?', 'J', 'N', 'K', 'V', '?', 'T', 'X',
 		'?', 'W'
 	};
 
-	static char symbols_lg[] = { 'A', 'B', 'C', 'H', 'F', 'G', 'Y' };
+	static const char symbols_lg[] = { 'A', 'B', 'C', 'H', 'F', 'G', 'Y' };
 
 	match_type = 0;
 	buf_pre[0] = 0;
@@ -766,8 +766,8 @@ static int isHexDigit(int c)
 static void copy_rule_string(char *string, int *state_out)
 {
 	// state 0: conditional, 1=pre, 2=match, 3=post, 4=phonemes
-	static char *outbuf[5] = { rule_cond, rule_pre, rule_match, rule_post, rule_phonemes };
-	static int next_state[5] = { 2, 2, 4, 4, 4 };
+	static char *const outbuf[5] = { rule_cond, rule_pre, rule_match, rule_post, rule_phonemes };
+	static const int next_state[5] = { 2, 2, 4, 4, 4 };
 	char *output;
 	char *p;
 	int ix;
diff --git a/src/libespeak-ng/dictionary.c b/src/libespeak-ng/dictionary.c
index a98caf54..51ce500a 100644
--- a/src/libespeak-ng/dictionary.c
+++ b/src/libespeak-ng/dictionary.c
@@ -1060,7 +1060,7 @@ void SetWordStress(Translator *tr, char *output, unsigned int *dictionary_flags,
 	char vowel_length[N_WORD_PHONEMES/2];
 	unsigned char phonetic[N_WORD_PHONEMES];
 
-	static char consonant_types[16] = { 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0 };
+	static const char consonant_types[16] = { 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0 };
 
 	stressflags = tr->langopts.stress_flags;
 
@@ -1226,9 +1226,9 @@ void SetWordStress(Translator *tr, char *output, unsigned int *dictionary_flags,
 		// LANG=Russian
 		if (stressed_syllable == 0) {
 			// no explicit stress - guess the stress from the number of syllables
-			static char guess_ru[16] =   { 0, 0, 1, 1, 2, 3, 3, 4, 5, 6, 7, 7, 8, 9, 10, 11 };
-			static char guess_ru_v[16] = { 0, 0, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 7, 8, 9, 10 }; // for final phoneme is a vowel
-			static char guess_ru_t[16] = { 0, 0, 1, 2, 3, 3, 3, 4, 5, 6, 7, 7, 7, 8, 9, 10 }; // for final phoneme is an unvoiced stop
+			static const char guess_ru[16] =   { 0, 0, 1, 1, 2, 3, 3, 4, 5, 6, 7, 7, 8, 9, 10, 11 };
+			static const char guess_ru_v[16] = { 0, 0, 1, 1, 2, 2, 3, 3, 4, 5, 6, 7, 7, 8, 9, 10 }; // for final phoneme is a vowel
+			static const char guess_ru_t[16] = { 0, 0, 1, 2, 3, 3, 3, 4, 5, 6, 7, 7, 7, 8, 9, 10 }; // for final phoneme is an unvoiced stop
 
 			stressed_syllable = vowel_count - 3;
 			if (vowel_count < 16) {
diff --git a/src/libespeak-ng/intonation.c b/src/libespeak-ng/intonation.c
index 4c9d54d9..d5e9092d 100644
--- a/src/libespeak-ng/intonation.c
+++ b/src/libespeak-ng/intonation.c
@@ -539,10 +539,10 @@ static int calc_pitch_segment(SYLLABLE *syllable_tab, int ix, int end_ix, TONE_H
 	int pitch_range;
 	int pitch_range_abs;
 	int *drops;
-	signed char *overflow_tab;
+	const signed char *overflow_tab;
 	SYLLABLE *syl;
 
-	static signed char continue_tab[5] = { -26, 32, 20, 8, 0 };
+	static const signed char continue_tab[5] = { -26, 32, 20, 8, 0 };
 
 	drops = th->body_drops;
 	pitch_range = (th->body_end - th->body_start) * 256;
diff --git a/src/libespeak-ng/klatt.c b/src/libespeak-ng/klatt.c
index b4f41059..29bf9d05 100644
--- a/src/libespeak-ng/klatt.c
+++ b/src/libespeak-ng/klatt.c
@@ -483,7 +483,7 @@ void KlattFini(void)
 static void frame_init(klatt_frame_ptr frame)
 {
 	double amp_par[7];
-	static double amp_par_factor[7] = { 0.6, 0.4, 0.15, 0.06, 0.04, 0.022, 0.03 };
+	static const double amp_par_factor[7] = { 0.6, 0.4, 0.15, 0.06, 0.04, 0.022, 0.03 };
 	long Gain0_tmp;
 	int ix;
 
@@ -552,7 +552,7 @@ static void frame_init(klatt_frame_ptr frame)
 
 static double impulsive_source()
 {
-	static double doublet[] = { 0.0, 13000000.0, -13000000.0 };
+	static const double doublet[] = { 0.0, 13000000.0, -13000000.0 };
 	static double vwave;
 
 	if (kt_globals.nper < 3)
@@ -623,7 +623,7 @@ static void pitch_synch_par_reset(klatt_frame_ptr frame)
 	long temp;
 	double temp1;
 	static long skew;
-	static short B0[224] = {
+	static const short B0[224] = {
 		1200, 1142, 1088, 1038, 991, 948, 907, 869, 833, 799, 768, 738, 710, 683, 658,
 		 634,  612,  590,  570, 551, 533, 515, 499, 483, 468, 454, 440, 427, 415, 403,
 		 391,  380,  370,  360, 350, 341, 332, 323, 315, 307, 300, 292, 285, 278, 272,
@@ -836,7 +836,7 @@ static double gen_noise(double noise)
 
 static double DBtoLIN(long dB)
 {
-	static short amptable[88] = {
+	static const short amptable[88] = {
 		   0,      0,     0,     0,     0,     0,     0,    0,     0,    0,   0,   0,  0, 6, 7,
 		   8,      9,    10,    11,    13,    14,    16,   18,    20,   22,  25,  28, 32,
 		   35,    40,    45,    51,    57,    64,    71,   80,    90,  101, 114, 128,
@@ -1076,10 +1076,10 @@ static void SetSynth_Klatt(int length, frame_t *fr1, frame_t *fr2, voice_t *wvoi
 void KlattInit()
 {
 
-	static short formant_hz[10] = { 280, 688, 1064, 2806, 3260, 3700, 6500, 7000, 8000, 280 };
-	static short bandwidth[10] = { 89, 160, 70, 160, 200, 200, 500, 500, 500, 89 };
-	static short parallel_amp[10] = { 0, 59, 59, 59, 59, 59, 59, 0, 0, 0 };
-	static short parallel_bw[10] = { 59, 59, 89, 149, 200, 200, 500, 0, 0, 0 };
+	static const short formant_hz[10] = { 280, 688, 1064, 2806, 3260, 3700, 6500, 7000, 8000, 280 };
+	static const short bandwidth[10] = { 89, 160, 70, 160, 200, 200, 500, 500, 500, 89 };
+	static const short parallel_amp[10] = { 0, 59, 59, 59, 59, 59, 59, 0, 0, 0 };
+	static const short parallel_bw[10] = { 59, 59, 89, 149, 200, 200, 500, 0, 0, 0 };
 
 	int ix;
 
diff --git a/src/libespeak-ng/numbers.c b/src/libespeak-ng/numbers.c
index 4c46768e..43123503 100644
--- a/src/libespeak-ng/numbers.c
+++ b/src/libespeak-ng/numbers.c
@@ -691,7 +691,7 @@ int TranslateLetter(Translator *tr, char *word, char *phonemes, int control, ALP
 	char ph_buf2[80];
 	char ph_alphabet[80];
 	char hexbuf[12];
-	static char pause_string[] = { phonPAUSE, 0 };
+	static const char pause_string[] = { phonPAUSE, 0 };
 
 	ph_buf[0] = 0;
 	ph_alphabet[0] = 0;
@@ -1039,7 +1039,7 @@ int TranslateRoman(Translator *tr, char *word, char *ph_out, WORD_TAB *wtab)
 	char number_chars[N_WORD_BYTES];
 
 	static const char *roman_numbers = "ixcmvld";
-	static int roman_values[] = { 1, 10, 100, 1000, 5, 50, 500 };
+	static const int roman_values[] = { 1, 10, 100, 1000, 5, 50, 500 };
 
 	acc = 0;
 	prev = 0;
diff --git a/src/libespeak-ng/phonemelist.c b/src/libespeak-ng/phonemelist.c
index 2860bf3a..850462a0 100644
--- a/src/libespeak-ng/phonemelist.c
+++ b/src/libespeak-ng/phonemelist.c
@@ -461,7 +461,7 @@ void MakePhonemeList(Translator *tr, int post_pause, bool start_sentence)
 		}
 
 		if ((plist3+1)->synthflags & SFLAG_LENGTHEN) {
-			static char types_double[] = { phFRICATIVE, phVFRICATIVE, phNASAL, phLIQUID, 0 };
+			static const char types_double[] = { phFRICATIVE, phVFRICATIVE, phNASAL, phLIQUID, 0 };
 			if ((j > 0) && (strchr(types_double, next->type))) {
 				// lengthen this consonant by doubling it
 				// BUT, can't insert a phoneme at position plist3[0] because it crashes PrevPh()
diff --git a/src/libespeak-ng/ssml.c b/src/libespeak-ng/ssml.c
index 3696f87a..ec49b204 100644
--- a/src/libespeak-ng/ssml.c
+++ b/src/libespeak-ng/ssml.c
@@ -275,13 +275,13 @@ static const char *VoiceFromStack(SSML_STACK *ssml_stack, int n_ssml_stack, espe
 }
 
 
-static wchar_t *GetSsmlAttribute(wchar_t *pw, const char *name)
+static const wchar_t *GetSsmlAttribute(wchar_t *pw, const char *name)
 {
 	// Gets the value string for an attribute.
 	// Returns NULL if the attribute is not present
 
 	int ix;
-	static wchar_t empty[1] = { 0 };
+	static const wchar_t empty[1] = { 0 };
 
 	while (*pw != 0) {
 		if (iswspace(pw[-1])) {
@@ -315,11 +315,11 @@ static int GetVoiceAttributes(wchar_t *pw, int tag_type, SSML_STACK *ssml_sp, SS
 	// a voice change.
 	// Returns  CLAUSE_TYPE_VOICE_CHANGE if there is a voice change
 
-	wchar_t *lang;
-	wchar_t *gender;
-	wchar_t *name;
-	wchar_t *age;
-	wchar_t *variant;
+	const wchar_t *lang;
+	const wchar_t *gender;
+	const wchar_t *name;
+	const wchar_t *age;
+	const wchar_t *variant;
 	int value;
 	const char *new_voice_id;
 
@@ -384,7 +384,7 @@ static void ProcessParamStack(char *outbuf, int *outix, int n_param_stack, PARAM
 	int value;
 	char buf[20];
 	int new_parameters[N_SPEECH_PARAM];
-	static char cmd_letter[N_SPEECH_PARAM] = { 0, 'S', 'A', 'P', 'R', 0, 'C', 0, 0, 0, 0, 0, 'F' }; // embedded command letters
+	static const char cmd_letter[N_SPEECH_PARAM] = { 0, 'S', 'A', 'P', 'R', 0, 'C', 0, 0, 0, 0, 0, 'F' }; // embedded command letters
 
 	for (param = 0; param < N_SPEECH_PARAM; param++)
 		new_parameters[param] = -1;
@@ -482,7 +482,7 @@ static int ReplaceKeyName(char *outbuf, int index, int *outix)
 	return 0;
 }
 
-static void SetProsodyParameter(int param_type, wchar_t *attr1, PARAM_STACK *sp, PARAM_STACK *param_stack, int *speech_parameters)
+static void SetProsodyParameter(int param_type, const wchar_t *attr1, PARAM_STACK *sp, PARAM_STACK *param_stack, int *speech_parameters)
 {
 	int value;
 	int sign;
@@ -564,9 +564,9 @@ int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, con
 	int value3;
 	int voice_change_flag;
 	wchar_t *px;
-	wchar_t *attr1;
-	wchar_t *attr2;
-	wchar_t *attr3;
+	const wchar_t *attr1;
+	const wchar_t *attr2;
+	const wchar_t *attr3;
 	int terminator;
 	char *uri;
 	int param_type;
@@ -581,7 +581,7 @@ int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, con
 		}
 
 	// these tags have no effect if they are self-closing, eg. <voice />
-	static char ignore_if_self_closing[] = { 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0 };
+	static const char ignore_if_self_closing[] = { 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0 };
 
 	bool self_closing = false;
 	int len;
@@ -711,13 +711,13 @@ int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, con
 			value = attrlookup(attr1, mnem_emphasis);
 
 		if (translator->langopts.tone_language == 1) {
-			static unsigned char emphasis_to_pitch_range[] = { 50, 50, 40, 70, 90, 100 };
-			static unsigned char emphasis_to_volume[] = { 100, 100, 70, 110, 135, 150 };
+			static const unsigned char emphasis_to_pitch_range[] = { 50, 50, 40, 70, 90, 100 };
+			static const unsigned char emphasis_to_volume[] = { 100, 100, 70, 110, 135, 150 };
 			// tone language (eg.Chinese) do emphasis by increasing the pitch range.
 			sp->parameter[espeakRANGE] = emphasis_to_pitch_range[value];
 			sp->parameter[espeakVOLUME] = emphasis_to_volume[value];
 		} else {
-			static unsigned char emphasis_to_volume2[] = { 100, 100, 75, 100, 120, 150 };
+			static const unsigned char emphasis_to_volume2[] = { 100, 100, 75, 100, 120, 150 };
 			sp->parameter[espeakVOLUME] = emphasis_to_volume2[value];
 			sp->parameter[espeakEMPHASIS] = value;
 		}
@@ -855,7 +855,7 @@ int ProcessSsmlTag(wchar_t *xml_buf, char *outbuf, int *outix, int n_outbuf, con
 		terminator = CLAUSE_NONE;
 
 		if ((attr1 = GetSsmlAttribute(px, "strength")) != NULL) {
-			static int break_value[6] = { 0, 7, 14, 21, 40, 80 }; // *10mS
+			static const int break_value[6] = { 0, 7, 14, 21, 40, 80 }; // *10mS
 			value = attrlookup(attr1, mnem_break);
 			if (value < 3) {
 				// adjust prepause on the following word
diff --git a/src/libespeak-ng/synthdata.c b/src/libespeak-ng/synthdata.c
index 128073a4..9db1b61b 100644
--- a/src/libespeak-ng/synthdata.c
+++ b/src/libespeak-ng/synthdata.c
@@ -428,7 +428,7 @@ static bool StressCondition(Translator *tr, PHONEME_LIST *plist, int condition,
 {
 	int stress_level;
 	PHONEME_LIST *pl;
-	static int condition_level[4] = { 1, 2, 4, 15 };
+	static const int condition_level[4] = { 1, 2, 4, 15 };
 
 	if (phoneme_tab[plist[0].phcode]->type == phVOWEL)
 		pl = plist;
diff --git a/src/libespeak-ng/synthesize.c b/src/libespeak-ng/synthesize.c
index 561de991..29789746 100644
--- a/src/libespeak-ng/synthesize.c
+++ b/src/libespeak-ng/synthesize.c
@@ -553,7 +553,7 @@ int FormantTransition2(frameref_t *seq, int *n_frames, unsigned int data1, unsig
 
 	#define N_VCOLOUR 2
 	// percentage change for each formant in 256ths
-	static short vcolouring[N_VCOLOUR][5] = {
+	static const short vcolouring[N_VCOLOUR][5] = {
 		{ 243, 272, 256, 256, 256 }, // palatal consonant follows
 		{ 256, 256, 240, 240, 240 }, // retroflex
 	};
diff --git a/src/libespeak-ng/tr_languages.c b/src/libespeak-ng/tr_languages.c
index 78d28952..d02d6c5a 100644
--- a/src/libespeak-ng/tr_languages.c
+++ b/src/libespeak-ng/tr_languages.c
@@ -1210,7 +1210,7 @@ Translator *SelectTranslator(const char *name)
 		break;
 	case L('m', 'k'): // Macedonian
 	{
-		static wchar_t vowels_cyrillic[] = {
+		static const wchar_t vowels_cyrillic[] = {
 			// also include 'р' [R]
 			0x440, 0x430, 0x435, 0x438, 0x439, 0x43e, 0x443, 0x44b, 0x44d,
 			0x44e, 0x44f, 0x450, 0x451, 0x456, 0x457, 0x45d, 0x45e, 0
@@ -1558,7 +1558,7 @@ Translator *SelectTranslator(const char *name)
 	{
 		static const short stress_lengths_vi[8] = { 150, 150,  180, 180,  210, 230,  230, 240 };
 		static const unsigned char stress_amps_vi[] = { 16, 16, 16, 16, 22, 22, 22, 22 };
-		static wchar_t vowels_vi[] = {
+		static const wchar_t vowels_vi[] = {
 			 0x61,   0xe0,   0xe1, 0x1ea3,   0xe3, 0x1ea1, // a
 			0x103, 0x1eb1, 0x1eaf, 0x1eb3, 0x1eb5, 0x1eb7, // ă
 			 0xe2, 0x1ea7, 0x1ea5, 0x1ea9, 0x1eab, 0x1ead, // â
diff --git a/src/libespeak-ng/voices.c b/src/libespeak-ng/voices.c
index 2b91859d..cc666158 100644
--- a/src/libespeak-ng/voices.c
+++ b/src/libespeak-ng/voices.c
@@ -356,10 +356,10 @@ void VoiceReset(int tone_only)
 	// Set voice to the default values
 
 	int pk;
-	static unsigned char default_heights[N_PEAKS] = { 130, 128, 120, 116, 100, 100, 128, 128, 128 }; // changed for v.1.47
-	static unsigned char default_widths[N_PEAKS] = { 140, 128, 128, 160, 171, 171, 128, 128, 128 };
+	static const unsigned char default_heights[N_PEAKS] = { 130, 128, 120, 116, 100, 100, 128, 128, 128 }; // changed for v.1.47
+	static const unsigned char default_widths[N_PEAKS] = { 140, 128, 128, 160, 171, 171, 128, 128, 128 };
 
-	static int breath_widths[N_PEAKS] = { 0, 200, 200, 400, 400, 400, 600, 600, 600 };
+	static const int breath_widths[N_PEAKS] = { 0, 200, 200, 400, 400, 400, 600, 600, 600 };
 
 	// default is:  pitch 80,118
 	voice->pitch_base = 0x47000;
diff --git a/src/libespeak-ng/wavegen.c b/src/libespeak-ng/wavegen.c
index 9441f201..271aa90c 100644
--- a/src/libespeak-ng/wavegen.c
+++ b/src/libespeak-ng/wavegen.c
@@ -1172,8 +1172,8 @@ static void SetSynth(int length, int modn, frame_t *fr1, frame_t *fr2, voice_t *
 	int length4;
 	int qix;
 	int cmd;
-	static int glottal_reduce_tab1[4] = { 0x30, 0x30, 0x40, 0x50 }; // vowel before [?], amp * 1/256
-	static int glottal_reduce_tab2[4] = { 0x90, 0xa0, 0xb0, 0xc0 }; // vowel after [?], amp * 1/256
+	static const int glottal_reduce_tab1[4] = { 0x30, 0x30, 0x40, 0x50 }; // vowel before [?], amp * 1/256
+	static const int glottal_reduce_tab2[4] = { 0x90, 0xa0, 0xb0, 0xc0 }; // vowel after [?], amp * 1/256
 
 	end_wave = 1;