diff --git a/examples/diffusionC.c b/examples/diffusionC.c
index 5e8404564..3a2ac6ab4 100644
--- a/examples/diffusionC.c
+++ b/examples/diffusionC.c
@@ -216,7 +216,7 @@ error(const double* u, const constants* c, double t)
 }
 
 static int
-usage()
+usage(void)
 {
   fprintf(stderr, "Usage: diffusionC [options]\n");
   fprintf(stderr, "Options:\n");
diff --git a/examples/iteratorC.c b/examples/iteratorC.c
index 8106c493a..93ef47259 100644
--- a/examples/iteratorC.c
+++ b/examples/iteratorC.c
@@ -30,7 +30,7 @@ void print3(cfp_iter1d begin, cfp_iter1d end)
     printf("%g\n", _.reference.get(_.iterator.ref(p)));
 }
 
-int main()
+int main(void)
 {
   const cfp_array1d_api _1d = cfp.array1d;
   const cfp_array2d_api _2d = cfp.array2d;
diff --git a/include/zfp.h b/include/zfp.h
index 9db4a3873..2d096cceb 100644
--- a/include/zfp.h
+++ b/include/zfp.h
@@ -335,7 +335,7 @@ zfp_stream_set_omp_chunk_size(
 
 /* unspecified configuration */
 zfp_config /* compression mode and parameter settings */
-zfp_config_none();
+zfp_config_none(void);
 
 /* fixed-rate configuration */
 zfp_config       /* compression mode and parameter settings */
@@ -358,7 +358,7 @@ zfp_config_accuracy(
 
 /* reversible (lossless) configuration */
 zfp_config /* compression mode and parameter settings */
-zfp_config_reversible();
+zfp_config_reversible(void);
 
 /* expert configuration */
 zfp_config      /* compression mode and parameter settings */
@@ -373,7 +373,7 @@ zfp_config_expert(
 
 /* allocate field struct */
 zfp_field* /* pointer to default initialized field */
-zfp_field_alloc();
+zfp_field_alloc(void);
 
 /* allocate metadata for 1D field f[nx] */
 zfp_field*       /* allocated field metadata */
diff --git a/include/zfp/bitstream.h b/include/zfp/bitstream.h
index 85922aadb..44598227e 100644
--- a/include/zfp/bitstream.h
+++ b/include/zfp/bitstream.h
@@ -34,7 +34,7 @@ void stream_close(bitstream* stream);
 bitstream* stream_clone(const bitstream* stream);
 
 /* word size in bits (equal to stream_word_bits) */
-bitstream_count stream_alignment();
+bitstream_count stream_alignment(void);
 
 /* pointer to beginning of stream */
 void* stream_data(const bitstream* stream);
diff --git a/include/zfp/bitstream.inl b/include/zfp/bitstream.inl
index 987f5a42a..80294ee9e 100644
--- a/include/zfp/bitstream.inl
+++ b/include/zfp/bitstream.inl
@@ -171,7 +171,7 @@ stream_write_word(bitstream* s, bitstream_word value)
 
 /* word size in bits (equals bitstream_word_bits) */
 inline_ bitstream_count
-stream_alignment()
+stream_alignment(void)
 {
   return wsize;
 }
diff --git a/include/zfp/internal/cfp/array1d.h b/include/zfp/internal/cfp/array1d.h
index 65bddff3b..fb20d3a77 100644
--- a/include/zfp/internal/cfp/array1d.h
+++ b/include/zfp/internal/cfp/array1d.h
@@ -96,7 +96,7 @@ typedef struct {
 } cfp_header1d_api;
 
 typedef struct {
-  cfp_array1d (*ctor_default)();
+  cfp_array1d (*ctor_default)(void);
   cfp_array1d (*ctor)(size_t n, double rate, const double* p, size_t cache_size);
   cfp_array1d (*ctor_copy)(const cfp_array1d src);
   cfp_array1d (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array1f.h b/include/zfp/internal/cfp/array1f.h
index 3f4d21e4f..6ca593d09 100644
--- a/include/zfp/internal/cfp/array1f.h
+++ b/include/zfp/internal/cfp/array1f.h
@@ -96,7 +96,7 @@ typedef struct {
 } cfp_header1f_api;
 
 typedef struct {
-  cfp_array1f (*ctor_default)();
+  cfp_array1f (*ctor_default)(void);
   cfp_array1f (*ctor)(size_t n, double rate, const float* p, size_t cache_size);
   cfp_array1f (*ctor_copy)(const cfp_array1f src);
   cfp_array1f (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array2d.h b/include/zfp/internal/cfp/array2d.h
index 9b070987d..b0e078af3 100644
--- a/include/zfp/internal/cfp/array2d.h
+++ b/include/zfp/internal/cfp/array2d.h
@@ -97,7 +97,7 @@ typedef struct {
 } cfp_header2d_api;
 
 typedef struct {
-  cfp_array2d (*ctor_default)();
+  cfp_array2d (*ctor_default)(void);
   cfp_array2d (*ctor)(size_t nx, size_t ny, double rate, const double* p, size_t cache_size);
   cfp_array2d (*ctor_copy)(const cfp_array2d src);
   cfp_array2d (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array2f.h b/include/zfp/internal/cfp/array2f.h
index 85bf584e7..0137b6094 100644
--- a/include/zfp/internal/cfp/array2f.h
+++ b/include/zfp/internal/cfp/array2f.h
@@ -97,7 +97,7 @@ typedef struct {
 } cfp_header2f_api;
 
 typedef struct {
-  cfp_array2f (*ctor_default)();
+  cfp_array2f (*ctor_default)(void);
   cfp_array2f (*ctor)(size_t nx, size_t ny, double rate, const float* p, size_t cache_size);
   cfp_array2f (*ctor_copy)(const cfp_array2f src);
   cfp_array2f (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array3d.h b/include/zfp/internal/cfp/array3d.h
index c3c337f6b..9c4a654a1 100644
--- a/include/zfp/internal/cfp/array3d.h
+++ b/include/zfp/internal/cfp/array3d.h
@@ -98,7 +98,7 @@ typedef struct {
 } cfp_header3d_api;
 
 typedef struct {
-  cfp_array3d (*ctor_default)();
+  cfp_array3d (*ctor_default)(void);
   cfp_array3d (*ctor)(size_t nx, size_t ny, size_t nz, double rate, const double* p, size_t cache_size);
   cfp_array3d (*ctor_copy)(const cfp_array3d src);
   cfp_array3d (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array3f.h b/include/zfp/internal/cfp/array3f.h
index 43fbe7229..e0f3aba5a 100644
--- a/include/zfp/internal/cfp/array3f.h
+++ b/include/zfp/internal/cfp/array3f.h
@@ -98,7 +98,7 @@ typedef struct {
 } cfp_header3f_api;
 
 typedef struct {
-  cfp_array3f (*ctor_default)();
+  cfp_array3f (*ctor_default)(void);
   cfp_array3f (*ctor)(size_t nx, size_t ny, size_t nz, double rate, const float* p, size_t cache_size);
   cfp_array3f (*ctor_copy)(const cfp_array3f src);
   cfp_array3f (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array4d.h b/include/zfp/internal/cfp/array4d.h
index 22e6a88fd..44d1ecf08 100644
--- a/include/zfp/internal/cfp/array4d.h
+++ b/include/zfp/internal/cfp/array4d.h
@@ -99,7 +99,7 @@ typedef struct {
 } cfp_header4d_api;
 
 typedef struct {
-  cfp_array4d (*ctor_default)();
+  cfp_array4d (*ctor_default)(void);
   cfp_array4d (*ctor)(size_t nx, size_t ny, size_t nz, size_t nw, double rate, const double* p, size_t cache_size);
   cfp_array4d (*ctor_copy)(const cfp_array4d src);
   cfp_array4d (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/include/zfp/internal/cfp/array4f.h b/include/zfp/internal/cfp/array4f.h
index b5e076748..b336dffe1 100644
--- a/include/zfp/internal/cfp/array4f.h
+++ b/include/zfp/internal/cfp/array4f.h
@@ -99,7 +99,7 @@ typedef struct {
 } cfp_header4f_api;
 
 typedef struct {
-  cfp_array4f (*ctor_default)();
+  cfp_array4f (*ctor_default)(void);
   cfp_array4f (*ctor)(size_t nx, size_t ny, size_t nz, size_t nw, double rate, const float* p, size_t cache_size);
   cfp_array4f (*ctor_copy)(const cfp_array4f src);
   cfp_array4f (*ctor_header)(const cfp_header h, const void* buffer, size_t buffer_size_bytes);
diff --git a/src/zfp.c b/src/zfp.c
index a498a985f..6192bd614 100644
--- a/src/zfp.c
+++ b/src/zfp.c
@@ -105,7 +105,7 @@ zfp_type_size(zfp_type type)
 /* public functions: fields ------------------------------------------------ */
 
 zfp_field*
-zfp_field_alloc()
+zfp_field_alloc(void)
 {
   zfp_field* field = (zfp_field*)malloc(sizeof(zfp_field));
   if (field) {
@@ -465,7 +465,7 @@ zfp_field_set_metadata(zfp_field* field, uint64 meta)
 /* public functions: compression mode and parameter settings --------------- */
 
 zfp_config
-zfp_config_none()
+zfp_config_none(void)
 {
   zfp_config config;
   config.mode = zfp_mode_null;
@@ -507,7 +507,7 @@ zfp_config_accuracy(
 }
 
 zfp_config
-zfp_config_reversible()
+zfp_config_reversible(void)
 {
   zfp_config config;
   config.mode = zfp_mode_reversible;
diff --git a/utils/zfp.c b/utils/zfp.c
index 3520f7437..1984532f5 100644
--- a/utils/zfp.c
+++ b/utils/zfp.c
@@ -80,7 +80,7 @@ print_error(const void* fin, const void* fout, zfp_type type, size_t n)
 }
 
 static void
-usage()
+usage(void)
 {
   fprintf(stderr, "%s\n", zfp_version_string);
   fprintf(stderr, "Usage: zfp <options>\n");