diff --git a/Makefile.am b/Makefile.am
index c7504e41fc..b152c92be5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -20,7 +20,7 @@ LIBJQ_SRC = src/builtin.c src/bytecode.c src/compile.c src/execute.c    \
 ### C build options
 
 AM_CFLAGS = -Wextra -Wall -Wno-unused-parameter -Wno-unused-function \
-            -Woverlength-strings
+            -Woverlength-strings -Wstrict-prototypes
 
 if WIN32
 AM_CFLAGS += -municode
diff --git a/src/builtin.c b/src/builtin.c
index c0aba960b0..e580993748 100644
--- a/src/builtin.c
+++ b/src/builtin.c
@@ -1924,7 +1924,7 @@ BINOPS
 
 // This is a hack to make last(g) yield no output values,
 // if g yields no output values, without using boxing.
-static block gen_last_1() {
+static block gen_last_1(void) {
   block last_var = gen_op_var_fresh(STOREV, "last");
   block is_empty_var = gen_op_var_fresh(STOREV, "is_empty");
   block init = BLOCK(gen_op_simple(DUP),
diff --git a/src/compile.c b/src/compile.c
index 0c208cad1d..618924a08a 100644
--- a/src/compile.c
+++ b/src/compile.c
@@ -129,7 +129,7 @@ block gen_location(location loc, struct locfile* l, block b) {
   return b;
 }
 
-block gen_noop() {
+block gen_noop(void) {
   block b = {0,0};
   return b;
 }
diff --git a/src/compile.h b/src/compile.h
index c1512e6b87..bef46328a7 100644
--- a/src/compile.h
+++ b/src/compile.h
@@ -16,7 +16,7 @@ typedef struct block {
 
 block gen_location(location, struct locfile*, block);
 
-block gen_noop();
+block gen_noop(void);
 int block_is_noop(block b);
 block gen_op_simple(opcode op);
 block gen_error(jv constant);
diff --git a/src/jq_test.c b/src/jq_test.c
index dd6920a420..df54be968f 100644
--- a/src/jq_test.c
+++ b/src/jq_test.c
@@ -8,11 +8,11 @@
 #include "jv.h"
 #include "jq.h"
 
-static void jv_test();
+static void jv_test(void);
 static void run_jq_tests(jv, int, FILE *, int, int);
-static void run_jq_start_state_tests();
+static void run_jq_start_state_tests(void);
 #ifdef HAVE_PTHREAD
-static void run_jq_pthread_tests();
+static void run_jq_pthread_tests(void);
 #endif
 
 int jq_testsuite(jv libdirs, int verbose, int argc, char* argv[]) {
@@ -307,7 +307,7 @@ static void test_jq_start_resets_state(char *prog, const char *input) {
   jq_teardown(&jq);
 }
 
-static void run_jq_start_state_tests() {
+static void run_jq_start_state_tests(void) {
   test_jq_start_resets_state(".[]", "[1,2,3]");
   test_jq_start_resets_state(".[] | if .%2 == 0 then halt_error else . end", "[1,2,3]");
 }
@@ -365,7 +365,7 @@ static void *test_pthread_run(void *ptr) {
     return NULL;
 }
 
-static void run_jq_pthread_tests() {
+static void run_jq_pthread_tests(void) {
     pthread_t threads[NUMBER_OF_THREADS];
     struct test_pthread_data data[NUMBER_OF_THREADS];
     int createerror;
@@ -395,7 +395,7 @@ static void run_jq_pthread_tests() {
 #endif // HAVE_PTHREAD
 
 
-static void jv_test() {
+static void jv_test(void) {
   /// JSON parser regression tests
   {
     jv v = jv_parse("{\"a':\"12\"}");
diff --git a/src/jv.c b/src/jv.c
index e7ae561975..cca63b9eb3 100644
--- a/src/jv.c
+++ b/src/jv.c
@@ -119,15 +119,15 @@ const jv JV_INVALID = {JVP_FLAGS_INVALID, 0, 0, 0, {0}};
 const jv JV_FALSE = {JVP_FLAGS_FALSE, 0, 0, 0, {0}};
 const jv JV_TRUE = {JVP_FLAGS_TRUE, 0, 0, 0, {0}};
 
-jv jv_true() {
+jv jv_true(void) {
   return JV_TRUE;
 }
 
-jv jv_false() {
+jv jv_false(void) {
   return JV_FALSE;
 }
 
-jv jv_null() {
+jv jv_null(void) {
   return JV_NULL;
 }
 
@@ -155,7 +155,7 @@ jv jv_invalid_with_msg(jv err) {
   return x;
 }
 
-jv jv_invalid() {
+jv jv_invalid(void) {
   return JV_INVALID;
 }
 
@@ -495,12 +495,12 @@ static pthread_once_t dec_ctx_once = PTHREAD_ONCE_INIT;
 
 // atexit finalizer to clean up the tsd dec contexts if main() exits
 // without having called pthread_exit()
-void jv_tsd_dec_ctx_fini() {
+void jv_tsd_dec_ctx_fini(void) {
   jv_mem_free(pthread_getspecific(dec_ctx_key));
   pthread_setspecific(dec_ctx_key, NULL);
 }
 
-void jv_tsd_dec_ctx_init() {
+void jv_tsd_dec_ctx_init(void) {
   if (pthread_key_create(&dec_ctx_key, jv_mem_free) != 0) {
     fprintf(stderr, "error: cannot create thread specific key");
     abort();
@@ -971,7 +971,7 @@ jv jv_array_sized(int n) {
   return jvp_array_new(n);
 }
 
-jv jv_array() {
+jv jv_array(void) {
   return jv_array_sized(16);
 }
 
@@ -1755,7 +1755,7 @@ static int jvp_object_contains(jv a, jv b) {
  * Objects (public interface)
  */
 #define DEFAULT_OBJECT_SIZE 8
-jv jv_object() {
+jv jv_object(void) {
   return jvp_object_new(8);
 }
 
diff --git a/src/jv_alloc.c b/src/jv_alloc.c
index 40c244c575..e84862565a 100644
--- a/src/jv_alloc.c
+++ b/src/jv_alloc.c
@@ -33,7 +33,7 @@ void jv_nomem_handler(jv_nomem_handler_f handler, void *data) {
   nomem_handler.handler = handler;
 }
 
-static void memory_exhausted() {
+static void memory_exhausted(void) {
   if (nomem_handler.handler)
     nomem_handler.handler(nomem_handler.data); // Maybe handler() will longjmp() to safety
   // Or not
@@ -104,7 +104,7 @@ void jv_nomem_handler(jv_nomem_handler_f handler, void *data) {
   nomem_handler->data = data;
 }
 
-static void memory_exhausted() {
+static void memory_exhausted(void) {
   struct nomem_handler *nomem_handler;
 
   pthread_once(&mem_once, tsd_init);
@@ -128,7 +128,7 @@ void jv_nomem_handler(jv_nomem_handler_f handler, void *data) {
   nomem_handler.data = data;
 }
 
-static void memory_exhausted() {
+static void memory_exhausted(void) {
   fprintf(stderr, "jq: error: cannot allocate memory\n");
   abort();
 }
diff --git a/src/jv_dtoa_tsd.c b/src/jv_dtoa_tsd.c
index 4bea31b565..c321f3db9c 100644
--- a/src/jv_dtoa_tsd.c
+++ b/src/jv_dtoa_tsd.c
@@ -19,7 +19,7 @@ static void tsd_dtoa_ctx_dtor(void *ctx) {
 #ifndef WIN32
 static
 #endif
-void jv_tsd_dtoa_ctx_fini() {
+void jv_tsd_dtoa_ctx_fini(void) {
   struct dtoa_context *ctx = pthread_getspecific(dtoa_ctx_key);
   tsd_dtoa_ctx_dtor(ctx);
   pthread_setspecific(dtoa_ctx_key, NULL);
@@ -28,7 +28,7 @@ void jv_tsd_dtoa_ctx_fini() {
 #ifndef WIN32
 static
 #endif
-void jv_tsd_dtoa_ctx_init() {
+void jv_tsd_dtoa_ctx_init(void) {
   if (pthread_key_create(&dtoa_ctx_key, tsd_dtoa_ctx_dtor) != 0) {
     fprintf(stderr, "error: cannot create thread specific key");
     abort();
@@ -36,7 +36,7 @@ void jv_tsd_dtoa_ctx_init() {
   atexit(jv_tsd_dtoa_ctx_fini);
 }
 
-inline struct dtoa_context *tsd_dtoa_context_get() {
+inline struct dtoa_context *tsd_dtoa_context_get(void) {
   pthread_once(&dtoa_ctx_once, jv_tsd_dtoa_ctx_init); // cannot fail
   struct dtoa_context *ctx = (struct dtoa_context*)pthread_getspecific(dtoa_ctx_key);
   if (!ctx) {
diff --git a/src/jv_dtoa_tsd.h b/src/jv_dtoa_tsd.h
index 2431d08e38..2af7c6deb0 100644
--- a/src/jv_dtoa_tsd.h
+++ b/src/jv_dtoa_tsd.h
@@ -1,4 +1,4 @@
 #ifndef JV_DTOA_TSD_H
 #define JV_DTOA_TSD_H
-struct dtoa_context *tsd_dtoa_context_get();
+struct dtoa_context *tsd_dtoa_context_get(void);
 #endif
diff --git a/src/main.c b/src/main.c
index a9a6ec54c2..7dddd26c37 100644
--- a/src/main.c
+++ b/src/main.c
@@ -117,7 +117,7 @@ static void usage(int code, int keep_it_short) {
   exit((ret < 0 && code == 0) ? 2 : code);
 }
 
-static void die() {
+static void die(void) {
   fprintf(stderr, "Use %s --help for help with command-line options,\n", progname);
   fprintf(stderr, "or see the jq manpage, or online docs  at https://jqlang.org\n");
   exit(2);
diff --git a/src/util.c b/src/util.c
index cfe65c4ae1..25bc5d5f88 100644
--- a/src/util.c
+++ b/src/util.c
@@ -98,7 +98,7 @@ jv expand_path(jv path) {
   return ret;
 }
 
-jv get_home() {
+jv get_home(void) {
   jv ret;
   char *home = getenv("HOME");
   if (!home) {