diff --git a/src/libespeak-ng/klatt.c b/src/libespeak-ng/klatt.c
index 3bbd1014..d8fae5eb 100644
--- a/src/libespeak-ng/klatt.c
+++ b/src/libespeak-ng/klatt.c
@@ -846,7 +846,7 @@ static int klattp[N_KLATTP];
 static double klattp1[N_KLATTP];
 static double klattp_inc[N_KLATTP];
 
-int Wavegen_Klatt(int resume)
+static int Wavegen_Klatt(int resume)
 {
 	int pk;
 	int x;
@@ -935,7 +935,7 @@ int Wavegen_Klatt(int resume)
 	return 0;
 }
 
-void SetSynth_Klatt(int length, frame_t *fr1, frame_t *fr2, voice_t *v, int control)
+static void SetSynth_Klatt(int length, frame_t *fr1, frame_t *fr2, voice_t *v, int control)
 {
 	int ix;
 	DOUBLEX next;
diff --git a/src/libespeak-ng/synthesize.h b/src/libespeak-ng/synthesize.h
index a2c52ea0..eb001848 100644
--- a/src/libespeak-ng/synthesize.h
+++ b/src/libespeak-ng/synthesize.h
@@ -545,7 +545,7 @@ int NumInstnWords(USHORT *prog);
 
 void InitBreath(void);
 
-void KlattInit();
+void KlattInit(void);
 void KlattReset(int control);
 int Wavegen_Klatt2(int length, int resume, frame_t *fr1, frame_t *fr2);