diff --git a/srv/format.c b/srv/format.c
index 11456a1..2694d02 100644
--- a/srv/format.c
+++ b/srv/format.c
@@ -17,12 +17,12 @@ struct BufferArg {
 	uint32_t byte_index;
 };
 
-uint32_t buffer_write(uint8_t byte, void* arg);
-uint32_t render_format(FormatCallback callback, void* arg,
+static uint32_t buffer_write(uint8_t byte, void* arg);
+static uint32_t render_format(FormatCallback callback, void* arg,
 		const char* restrict format, va_list va);
-uint32_t render_signed(FormatCallback callback, void* arg,
+static uint32_t render_signed(FormatCallback callback, void* arg,
 		int32_t number, uint8_t base);
-uint32_t render_unsigned(FormatCallback callback, void* arg,
+static uint32_t render_unsigned(FormatCallback callback, void* arg,
 		uint32_t number, uint8_t base);
 
 
@@ -59,7 +59,7 @@ uint32_t format_vfctprintf(FormatCallback callback, void* arg,
 
 //--local functions-------------------------------------------------------------
 
-uint32_t buffer_write(uint8_t byte, void* arg)
+static uint32_t buffer_write(uint8_t byte, void* arg)
 {
 	struct BufferArg* buffer_arg = (struct BufferArg*)arg;
 	if (buffer_arg->byte_index >= buffer_arg->buffer_size) {
@@ -71,7 +71,7 @@ uint32_t buffer_write(uint8_t byte, void* arg)
 	return 0;
 }
 
-uint32_t render_format(FormatCallback callback, void* arg,
+static uint32_t render_format(FormatCallback callback, void* arg,
 		const char* restrict format, va_list va)
 {
 	bool in_format = false;
@@ -124,7 +124,7 @@ uint32_t render_format(FormatCallback callback, void* arg,
 	return 0;
 }
 
-uint32_t render_signed(FormatCallback callback, void* arg,
+static uint32_t render_signed(FormatCallback callback, void* arg,
 		int32_t number, uint8_t base)
 {
 	if (number < 0) {
@@ -135,7 +135,7 @@ uint32_t render_signed(FormatCallback callback, void* arg,
 	return render_unsigned(callback, arg, (uint32_t)number, base);
 }
 
-uint32_t render_unsigned(FormatCallback callback, void* arg,
+static uint32_t render_unsigned(FormatCallback callback, void* arg,
 		 uint32_t number, uint8_t base)
 {
 	uint32_t base_power = base;