diff --git a/lib/aligned_malloc.h b/lib/aligned_malloc.h
index ee6e7b8..f301a0e 100644
--- a/lib/aligned_malloc.h
+++ b/lib/aligned_malloc.h
@@ -7,7 +7,7 @@
 
 #include "lib_common.h"
 
-extern void *aligned_malloc(size_t alignment, size_t size);
-extern void aligned_free(void *ptr);
+void *aligned_malloc(size_t alignment, size_t size);
+void aligned_free(void *ptr);
 
 #endif /* LIB_ALIGNED_MALLOC_H */
diff --git a/lib/arm/cpu_features.h b/lib/arm/cpu_features.h
index 390d96c..dae3b89 100644
--- a/lib/arm/cpu_features.h
+++ b/lib/arm/cpu_features.h
@@ -23,7 +23,7 @@
 
 extern volatile u32 _cpu_features;
 
-extern void setup_cpu_features(void);
+void setup_cpu_features(void);
 
 static inline u32 get_cpu_features(void)
 {
diff --git a/lib/deflate_compress.h b/lib/deflate_compress.h
index f4bb23b..d97d019 100644
--- a/lib/deflate_compress.h
+++ b/lib/deflate_compress.h
@@ -8,7 +8,6 @@
 
 struct libdeflate_compressor;
 
-extern unsigned int
-deflate_get_compression_level(struct libdeflate_compressor *c);
+unsigned int deflate_get_compression_level(struct libdeflate_compressor *c);
 
 #endif /* LIB_DEFLATE_COMPRESS_H */
diff --git a/lib/x86/cpu_features.h b/lib/x86/cpu_features.h
index b224181..a2ad544 100644
--- a/lib/x86/cpu_features.h
+++ b/lib/x86/cpu_features.h
@@ -27,7 +27,7 @@
 
 extern volatile u32 _cpu_features;
 
-extern void setup_cpu_features(void);
+void setup_cpu_features(void);
 
 static inline u32 get_cpu_features(void)
 {
diff --git a/programs/prog_util.h b/programs/prog_util.h
index 0265dd0..66d8cf1 100644
--- a/programs/prog_util.h
+++ b/programs/prog_util.h
@@ -57,7 +57,7 @@
  */
 
 #include <wchar.h>
-extern int wmain(int argc, wchar_t **argv);
+int wmain(int argc, wchar_t **argv);
 #  define	tmain		wmain
 #  define	tchar		wchar_t
 #  define	_T(text)	L##text
@@ -116,12 +116,12 @@ extern int wmain(int argc, wchar_t **argv);
 
 extern const tchar *program_invocation_name;
 
-extern void _printf(1, 2) msg(const char *fmt, ...);
-extern void _printf(1, 2) msg_errno(const char *fmt, ...);
+void _printf(1, 2) msg(const char *fmt, ...);
+void _printf(1, 2) msg_errno(const char *fmt, ...);
 
-extern void *xmalloc(size_t size);
+void *xmalloc(size_t size);
 
-extern const tchar *get_filename(const tchar *path);
+const tchar *get_filename(const tchar *path);
 
 struct file_stream {
 	int fd;
@@ -132,27 +132,26 @@ struct file_stream {
 	size_t mmap_size;
 };
 
-extern int xopen_for_read(const tchar *path, bool symlink_ok,
-			  struct file_stream *strm);
-extern int xopen_for_write(const tchar *path, bool force,
-			   struct file_stream *strm);
-extern int map_file_contents(struct file_stream *strm, u64 size);
+int xopen_for_read(const tchar *path, bool symlink_ok,
+		   struct file_stream *strm);
+int xopen_for_write(const tchar *path, bool force, struct file_stream *strm);
+int map_file_contents(struct file_stream *strm, u64 size);
 
-extern ssize_t xread(struct file_stream *strm, void *buf, size_t count);
-extern int full_write(struct file_stream *strm, const void *buf, size_t count);
+ssize_t xread(struct file_stream *strm, void *buf, size_t count);
+int full_write(struct file_stream *strm, const void *buf, size_t count);
 
-extern int xclose(struct file_stream *strm);
+int xclose(struct file_stream *strm);
 
-extern int parse_compression_level(tchar opt_char, const tchar *arg);
+int parse_compression_level(tchar opt_char, const tchar *arg);
 
-extern struct libdeflate_compressor *alloc_compressor(int level);
-extern struct libdeflate_decompressor *alloc_decompressor(void);
+struct libdeflate_compressor *alloc_compressor(int level);
+struct libdeflate_decompressor *alloc_decompressor(void);
 
 /* tgetopt.c */
 
 extern tchar *toptarg;
 extern int toptind, topterr, toptopt;
 
-extern int tgetopt(int argc, tchar *argv[], const tchar *optstring);
+int tgetopt(int argc, tchar *argv[], const tchar *optstring);
 
 #endif /* PROGRAMS_PROG_UTIL_H */
diff --git a/programs/test_util.h b/programs/test_util.h
index 10f025a..e10c154 100644
--- a/programs/test_util.h
+++ b/programs/test_util.h
@@ -38,21 +38,21 @@
 # define _noreturn
 #endif
 
-extern void _noreturn
+void _noreturn
 assertion_failed(const char *expr, const char *file, int line);
 
 #define ASSERT(expr) { if (unlikely(!(expr))) \
 	assertion_failed(#expr, __FILE__, __LINE__); }
 
-extern void begin_performance_test(void);
+void begin_performance_test(void);
 
-extern void alloc_guarded_buffer(size_t size, u8 **start_ret, u8 **end_ret);
-extern void free_guarded_buffer(u8 *start, u8 *end);
+void alloc_guarded_buffer(size_t size, u8 **start_ret, u8 **end_ret);
+void free_guarded_buffer(u8 *start, u8 *end);
 
-extern u64 timer_ticks(void);
-extern u64 timer_ticks_to_ms(u64 ticks);
-extern u64 timer_MB_per_s(u64 bytes, u64 ticks);
-extern u64 timer_KB_per_s(u64 bytes, u64 ticks);
+u64 timer_ticks(void);
+u64 timer_ticks_to_ms(u64 ticks);
+u64 timer_MB_per_s(u64 bytes, u64 ticks);
+u64 timer_KB_per_s(u64 bytes, u64 ticks);
 
 struct output_bitstream {
 	machine_word_t bitbuf;
@@ -61,8 +61,7 @@ struct output_bitstream {
 	u8 *end;
 };
 
-extern bool put_bits(struct output_bitstream *os, machine_word_t bits,
-		     int num_bits);
-extern bool flush_bits(struct output_bitstream *os);
+bool put_bits(struct output_bitstream *os, machine_word_t bits, int num_bits);
+bool flush_bits(struct output_bitstream *os);
 
 #endif /* PROGRAMS_TEST_UTIL_H */