diff --git a/configure.ac b/configure.ac
index f51c54ee..273889d8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -277,6 +277,8 @@ dnl ================================================================
 
 AX_CHECK_COMPILE_FLAG([-Wunused-function], [CFLAGS="-Wunused-function $CFLAGS"])
 
+AX_CHECK_COMPILE_FLAG([-Wunused-parameter], [CFLAGS="-Wunused-parameter $CFLAGS"])
+
 dnl ================================================================
 dnl Generate output.
 dnl ================================================================
diff --git a/src/libespeak-ng/encoding.c b/src/libespeak-ng/encoding.c
index 122e9099..2084e5f3 100644
--- a/src/libespeak-ng/encoding.c
+++ b/src/libespeak-ng/encoding.c
@@ -654,6 +654,7 @@ string_decoder_getc_auto(espeak_ng_TEXT_DECODER *decoder)
 static uint32_t
 null_decoder_getc(espeak_ng_TEXT_DECODER *decoder)
 {
+	(void)decoder; // unused parameter
 	return 0;
 }
 
diff --git a/src/libespeak-ng/synth_mbrola.c b/src/libespeak-ng/synth_mbrola.c
index 3e2031dc..f9bd3a3a 100644
--- a/src/libespeak-ng/synth_mbrola.c
+++ b/src/libespeak-ng/synth_mbrola.c
@@ -573,16 +573,25 @@ void MbrolaReset(void)
 
 espeak_ng_STATUS LoadMbrolaTable(const char *mbrola_voice, const char *phtrans, int *srate)
 {
+	(void)mbrola_voice; // unused parameter
+	(void)phtrans; // unused parameter
+	(void)srate; // unused parameter
 	return ENS_NOT_SUPPORTED;
 }
 
 int MbrolaGenerate(PHONEME_LIST *phoneme_list, int *n_ph, int resume)
 {
+	(void)phoneme_list; // unused parameter
+	(void)n_ph; // unused parameter
+	(void)resume; // unused parameter
 	return 0;
 }
 
 int MbrolaFill(int length, int resume, int amplitude)
 {
+	(void)length; // unused parameter
+	(void)resume; // unused parameter
+	(void)amplitude; // unused parameter
 	return 0;
 }
 
diff --git a/tests/api.c b/tests/api.c
index 6a509711..9a48859e 100644
--- a/tests/api.c
+++ b/tests/api.c
@@ -540,6 +540,8 @@ test_espeak_set_voice_by_properties_with_invalid_language()
 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+
 	char *progdir = strdup(argv[0]);
 	char *dir = strrchr(progdir, '/');
 	if (dir != NULL) *dir = 0;
diff --git a/tests/encoding.c b/tests/encoding.c
index 3a141051..52dffe2e 100644
--- a/tests/encoding.c
+++ b/tests/encoding.c
@@ -876,6 +876,9 @@ test_peekc()
 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+	(void)argv; // unused parameter
+
 	test_unbound_text_decoder();
 	test_unknown_encoding();
 
diff --git a/tests/readclause.c b/tests/readclause.c
index e0002c4d..486c0979 100644
--- a/tests/readclause.c
+++ b/tests/readclause.c
@@ -513,6 +513,9 @@ test_uts51_emoji_keycap_sequence()
 int
 main(int argc, char **argv)
 {
+	(void)argc; // unused parameter
+	(void)argv; // unused parameter
+
 	assert(espeak_Initialize(AUDIO_OUTPUT_SYNCHRONOUS, 0, NULL, espeakINITIALIZE_DONT_EXIT) == 22050);
 
 	test_latin();