diff --git a/pffft/pffft_double.h b/pffft/pffft_double.h
index afa8de0..f4571b4 100644
--- a/pffft/pffft_double.h
+++ b/pffft/pffft_double.h
@@ -186,10 +186,10 @@ extern "C" {
   void pffftd_zconvolve_no_accu(PFFFTD_Setup *setup, const double *dft_a, const double *dft_b, double*dft_ab, double scaling);
 
   /* return 4 or 1 wether support AVX instructions was enabled when building pffft-double.c */
-  int pffftd_simd_size();
+  int pffftd_simd_size(void);
 
   /* return string identifier of used architecture (AVX/..) */
-  const char * pffftd_simd_arch();
+  const char * pffftd_simd_arch(void);
 
   /* simple helper to get minimum possible fft size */
   int pffftd_min_fft_size(pffft_transform_t transform);
diff --git a/pffft/pffft_priv_impl.h b/pffft/pffft_priv_impl.h
index e92fdc8..bdc13c2 100644
--- a/pffft/pffft_priv_impl.h
+++ b/pffft/pffft_priv_impl.h
@@ -69,7 +69,7 @@
 #endif
 
 
-int FUNC_SIMD_SIZE() { return SIMD_SZ; }
+int FUNC_SIMD_SIZE(void) { return SIMD_SZ; }
 
 int FUNC_MIN_FFT_SIZE(pffft_transform_t transform) {
   /* unfortunately, the fft size must be a multiple of 16 for complex FFTs
@@ -109,7 +109,7 @@ int FUNC_NEAREST_SIZE(int N, pffft_transform_t cplx, int higher) {
       return N;
 }
 
-const char * FUNC_SIMD_ARCH() { return VARCH; }
+const char * FUNC_SIMD_ARCH(void) { return VARCH; }
 
 
 /*
@@ -1821,7 +1821,7 @@ void FUNC_TRANSFORM_ORDERED(SETUP_STRUCT *setup, const float *input, float *outp
 #define assertv4(v,f0,f1,f2,f3) assert(v.f[0] == (f0) && v.f[1] == (f1) && v.f[2] == (f2) && v.f[3] == (f3))
 
 /* detect bugs with the vector support macros */
-void FUNC_VALIDATE_SIMD_A() {
+void FUNC_VALIDATE_SIMD_A(void) {
   float f[16] = { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15 };
   v4sf_union a0, a1, a2, a3, t, u; 
   memcpy(a0.f, f, 4*sizeof(float));
@@ -2220,7 +2220,7 @@ int FUNC_VALIDATE_SIMD_EX(FILE * DbgOut)
 
 #else  /* if ( SIMD_SZ == 4 ) */
 
-void FUNC_VALIDATE_SIMD_A()
+void FUNC_VALIDATE_SIMD_A(void)
 {
 }
 
diff --git a/pffft/simd/pf_scalar_double.h b/pffft/simd/pf_scalar_double.h
index b7a1cae..7d555cc 100644
--- a/pffft/simd/pf_scalar_double.h
+++ b/pffft/simd/pf_scalar_double.h
@@ -58,7 +58,7 @@ typedef union v4sf_union {
 #  define VARCH "4xScalar"
 #  define VREQUIRES_ALIGN 0
 
-  static ALWAYS_INLINE(v4sf) VZERO() {
+  static ALWAYS_INLINE(v4sf) VZERO(void) {
     v4sf r = { 0.f, 0.f, 0.f, 0.f };
     return r;
   }