diff --git a/Makefile b/Makefile
index d59fcc7..83245df 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,8 @@
 .PHONY: all clean test
 
-LDFLAGS=-O2 -Wall -fPIC
-CFLAGS=-O2 -Wall -fPIC -I. -Wno-unused-function
+LDFLAGS=-O2 -fPIC
+CFLAGS=-O2 -std=gnu11 -Wall -Wextra -fPIC -I. \
+       -Wno-unused-function -Wno-missing-field-initializers -Wno-unused-parameter
 ifneq (,$(findstring gcc, $(CC)))
 	# gcc's maybe-unintialized is too imprecise, disable it.
 	# clang disbles this functionality by default and doesn't recognize the flag.
diff --git a/capn-malloc.c b/capn-malloc.c
index 5f392b6..ced44f4 100644
--- a/capn-malloc.c
+++ b/capn-malloc.c
@@ -190,7 +190,7 @@ static void header_calc(struct capn *c, uint32_t *headerlen, size_t *headersz)
 
 static int header_render(struct capn *c, struct capn_segment *seg, uint32_t *header, uint32_t headerlen, size_t *datasz)
 {
-	int i;
+	size_t i;
 
 	header[0] = capn_flip32(c->segnum - 1);
 	header[headerlen-1] = 0; /* Zero out the spare position in the header sizes */
@@ -291,8 +291,8 @@ capn_write_mem(struct capn *c, uint8_t *p, size_t sz, int packed)
 
 static int _write_fd(ssize_t (*write_fd)(int fd, void *p, size_t count), int fd, void *p, size_t count)
 {
-	int ret;
-	int sent = 0;
+	ssize_t ret;
+	size_t sent = 0;
 
 	while (sent < count) {
 		ret = write_fd(fd, ((uint8_t*)p)+sent, count-sent);
diff --git a/capn-stream.c b/capn-stream.c
index bfd607d..551a5a3 100644
--- a/capn-stream.c
+++ b/capn-stream.c
@@ -12,7 +12,8 @@ int capn_deflate(struct capn_stream* s) {
 	}
 
 	while (s->avail_in) {
-		int i, sz;
+		int i;
+		size_t sz;
 		uint8_t hdr = 0;
 		uint8_t *p;
 
@@ -105,7 +106,8 @@ int capn_inflate(struct capn_stream* s) {
 	}
 
 	while (s->avail_out) {
-		int i, sz;
+		int i;
+		size_t sz;
 		uint8_t hdr;
 
 		if (s->zeros > 0) {
diff --git a/capn.c b/capn.c
index 9ae5633..d9109b3 100644
--- a/capn.c
+++ b/capn.c
@@ -1034,10 +1034,10 @@ capn_ptr capn_new_ptr_list(struct capn_segment *seg, int sz) {
 	return p;
 }
 
-capn_ptr capn_new_string(struct capn_segment *seg, const char *str, int sz) {
+capn_ptr capn_new_string(struct capn_segment *seg, const char *str, ssize_t sz) {
 	capn_ptr p = {CAPN_LIST};
 	p.seg = seg;
-	p.len = ((sz >= 0) ? sz : strlen(str)) + 1;
+	p.len = ((sz >= 0) ? (size_t)sz : strlen(str)) + 1;
 	p.datasz = 1;
 	new_object(&p, p.len);
 	if (p.data) {
diff --git a/compiler/capnpc-c.c b/compiler/capnpc-c.c
index 42f0d3a..f4d8580 100644
--- a/compiler/capnpc-c.c
+++ b/compiler/capnpc-c.c
@@ -656,7 +656,7 @@ static const char *field_name(struct field *f) {
 		"_Thread_local",
 	};
 
-	int i;
+	size_t i;
 	const char *s = f->f.name.str;
 	for (i = 0; i < sizeof(reserved)/sizeof(reserved[0]); i++) {
 		if (!strcmp(s, reserved[i])) {
@@ -1248,13 +1248,14 @@ int main() {
 			fprintf(srcf, "static const capn_ptr capn_null = {CAPN_NULL};\n");
 
 		if (g_valseg.len > 8) {
+			size_t k;
 			fprintf(srcf, "static const uint8_t capn_buf[%lu] = {", g_valseg.len-8);
-			for (j = 8; j < g_valseg.len; j++) {
-				if (j > 8)
+			for (k = 8; k < g_valseg.len; k++) {
+				if (k > 8)
 					fprintf(srcf, ",");
-				if ((j % 8) == 0)
+				if ((k % 8) == 0)
 					fprintf(srcf, "\n\t");
-				fprintf(srcf, "%u", ((uint8_t*)g_valseg.data)[j]);
+				fprintf(srcf, "%u", ((uint8_t*)g_valseg.data)[k]);
 			}
 			fprintf(srcf, "\n};\n");