diff --git a/src/gpujpeg_common.c b/src/gpujpeg_common.c
index 6d288cd..15ddc22 100644
--- a/src/gpujpeg_common.c
+++ b/src/gpujpeg_common.c
@@ -125,7 +125,7 @@ static const struct {
 
 /* Documented at declaration */
 struct gpujpeg_devices_info
-gpujpeg_get_devices_info()
+gpujpeg_get_devices_info(void)
 {
     struct gpujpeg_devices_info devices_info = { 0 };
 
@@ -163,7 +163,7 @@ gpujpeg_get_devices_info()
 
 /* Documented at declaration */
 int
-gpujpeg_print_devices_info()
+gpujpeg_print_devices_info(void)
 {
     struct gpujpeg_devices_info devices_info = gpujpeg_get_devices_info();
     if ( devices_info.device_count == 0 ) {
@@ -766,7 +766,7 @@ gpujpeg_coder_init_image(struct gpujpeg_coder * coder, const struct gpujpeg_para
     }
     // Check data size
     //printf("%d == %d\n", coder->data_size, data_index);
-    assert(coder->data_size == data_index);
+    assert(coder->data_size == data_index); (void) data_index;
     // Set compressed size
     coder->data_compressed_size = data_compressed_index;
     //printf("Compressed size %d (segments %d)\n", coder->data_compressed_size, coder->segment_count);
@@ -1719,7 +1719,7 @@ gpujpeg_opengl_texture_unmap(struct gpujpeg_opengl_texture* texture)
 #endif
 }
 
-int gpujpeg_version()
+int gpujpeg_version(void)
 {
 #ifdef HAVE_GPUJPEG_VERSION_H
     return GPUJPEG_VERSION_INT;
diff --git a/src/gpujpeg_dct_cpu.c b/src/gpujpeg_dct_cpu.c
index 5e1ce1c..bf6d912 100644
--- a/src/gpujpeg_dct_cpu.c
+++ b/src/gpujpeg_dct_cpu.c
@@ -191,7 +191,7 @@ void gpujpeg_idct_cpu_perform(int16_t* block, int16_t* table)
 /**
  * Init inverse DCT
  */
-void gpujpeg_idct_cpu_init()
+void gpujpeg_idct_cpu_init(void)
 {
     iclp = iclip + 512;
     for ( int i = -512; i < 512; i++ )
diff --git a/src/gpujpeg_encoder.c b/src/gpujpeg_encoder.c
index 86ebfd4..50bd1ce 100644
--- a/src/gpujpeg_encoder.c
+++ b/src/gpujpeg_encoder.c
@@ -84,7 +84,7 @@ gpujpeg_encoder_create(cudaStream_t stream)
     int result = 1;
 
     // Create writer
-    encoder->writer = gpujpeg_writer_create(encoder);
+    encoder->writer = gpujpeg_writer_create();
     if ( encoder->writer == NULL )
         result = 0;
 
diff --git a/src/gpujpeg_huffman_gpu_decoder.h b/src/gpujpeg_huffman_gpu_decoder.h
index 74b21ef..ff1a14d 100644
--- a/src/gpujpeg_huffman_gpu_decoder.h
+++ b/src/gpujpeg_huffman_gpu_decoder.h
@@ -45,7 +45,7 @@ struct gpujpeg_huffman_gpu_decoder;
  * @return 0 if succeeds, otherwise nonzero
  */
 struct gpujpeg_huffman_gpu_decoder *
-gpujpeg_huffman_gpu_decoder_init();
+gpujpeg_huffman_gpu_decoder_init(void);
 
 void
 gpujpeg_huffman_gpu_decoder_destroy(struct gpujpeg_huffman_gpu_decoder *);
diff --git a/src/gpujpeg_reader.c b/src/gpujpeg_reader.c
index 0241d40..81c8671 100644
--- a/src/gpujpeg_reader.c
+++ b/src/gpujpeg_reader.c
@@ -89,7 +89,7 @@ struct gpujpeg_reader
 
 /* Documented at declaration */
 struct gpujpeg_reader*
-gpujpeg_reader_create()
+gpujpeg_reader_create(void)
 {
     struct gpujpeg_reader* reader = (struct gpujpeg_reader*)
             malloc(sizeof(struct gpujpeg_reader));
diff --git a/src/gpujpeg_reader.h b/src/gpujpeg_reader.h
index d3aa987..aa7b613 100644
--- a/src/gpujpeg_reader.h
+++ b/src/gpujpeg_reader.h
@@ -47,7 +47,7 @@ struct gpujpeg_reader;
  * @return reader structure if succeeds, otherwise NULL
  */
 struct gpujpeg_reader*
-gpujpeg_reader_create();
+gpujpeg_reader_create(void);
 
 /**
  * Destroy JPEG reader
diff --git a/src/gpujpeg_writer.c b/src/gpujpeg_writer.c
index d72bde8..585f6ef 100644
--- a/src/gpujpeg_writer.c
+++ b/src/gpujpeg_writer.c
@@ -40,7 +40,7 @@
 
 /* Documented at declaration */
 struct gpujpeg_writer*
-gpujpeg_writer_create()
+gpujpeg_writer_create(void)
 {
     struct gpujpeg_writer* writer = (struct gpujpeg_writer*) malloc(sizeof(struct gpujpeg_writer));
     if (writer == NULL) {
diff --git a/src/gpujpeg_writer.h b/src/gpujpeg_writer.h
index 019acea..55be894 100644
--- a/src/gpujpeg_writer.h
+++ b/src/gpujpeg_writer.h
@@ -68,7 +68,7 @@ struct gpujpeg_writer
  * @return writer structure if succeeds, otherwise NULL
  */
 struct gpujpeg_writer*
-gpujpeg_writer_create();
+gpujpeg_writer_create(void);
 
 /**
  * Init JPEG writer.