diff --git a/capn-stream.c b/capn-stream.c
index b734dc7..bfd607d 100644
--- a/capn-stream.c
+++ b/capn-stream.c
@@ -80,7 +80,7 @@ int capn_deflate(struct capn_stream* s) {
 			continue;
 
 		default:
-			if (s->avail_out < 1 + sz)
+			if (s->avail_out < 1U + sz)
 				return CAPN_NEED_MORE;
 
 			*(s->next_out++) = hdr;
@@ -167,7 +167,7 @@ int capn_inflate(struct capn_stream* s) {
 				if (hdr & (1 << i))
 					sz++;
 			}
-			if (s->avail_in < 1 + sz)
+			if (s->avail_in < 1U + sz)
 				return CAPN_NEED_MORE;
 
 			s->next_in += 1;
diff --git a/capn-test.cpp b/capn-test.cpp
index cf76bc0..b9a0b9f 100644
--- a/capn-test.cpp
+++ b/capn-test.cpp
@@ -274,11 +274,11 @@ static void getSegments(struct capn *c, struct capn_segment **s, size_t num) {
   ASSERT_EQ(num, c->segnum);
 
   s[0] = c->seglist;
-  for (unsigned i = 1; i < num; i++) {
+  for (size_t i = 1; i < num; i++) {
     s[i] = s[i-1]->next;
   }
 
-  for (unsigned i = 0; i < num; i++) {
+  for (size_t i = 0; i < num; i++) {
     EXPECT_EQ(s[i]->id, i);
   }
 }
@@ -315,7 +315,7 @@ TEST(WireFormat, StructRoundTrip_OneSegmentPerAllocation) {
 
   struct capn ctx2;
   memset(&ctx2, 0, sizeof(ctx2));
-  for (unsigned i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
+  for (size_t i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
     capn_append_segment(&ctx2, segments[i]);
   }
 
@@ -371,7 +371,7 @@ TEST(WireFormat, StructRoundTrip_OneSegmentPerAllocation_NoTag) {
 
   struct capn ctx2;
   memset(&ctx2, 0, sizeof(ctx2));
-  for (unsigned i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
+  for (size_t i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
     capn_append_segment(&ctx2, segments[i]);
   }
 
@@ -421,7 +421,7 @@ TEST(WireFormat, StructRoundTrip_MultipleSegmentsWithMultipleAllocations) {
 
   struct capn ctx2;
   memset(&ctx2, 0, sizeof(ctx2));
-  for (unsigned i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
+  for (size_t i = 0; i < sizeof(segments)/sizeof(segments[0]); i++) {
     capn_append_segment(&ctx2, segments[i]);
   }
 
diff --git a/capn.c b/capn.c
index 256755a..9ae5633 100644
--- a/capn.c
+++ b/capn.c
@@ -186,7 +186,7 @@ end:
 }
 
 static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *s, uint32_t id) {
-	struct capn_tree **x = &c->segtree;
+	struct capn_tree **x;
 	struct capn_segment *y = NULL;
 
 	if (s && s->id == id)
@@ -195,6 +195,7 @@ static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *
 		return NULL;
 
 	if (id < c->segnum) {
+		x = &c->segtree;
 		while (*x) {
 			y = (struct capn_segment*) *x;
 			if (id == y->id) {
@@ -205,6 +206,9 @@ static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *
 				x = &y->hdr.link[1];
 			}
 		}
+	} else {
+		/* Otherwise `x` may be uninitialized */
+		return NULL;
 	}
 
 	s = c->lookup ? c->lookup(c->user, id) : NULL;
@@ -229,7 +233,7 @@ static struct capn_segment *lookup_segment(struct capn* c, struct capn_segment *
 
 static uint64_t lookup_double(struct capn_segment **s, char **d, uint64_t val) {
 	uint64_t far, tag;
-	uint32_t off = (U32(val) >> 3) * 8;
+	size_t off = (U32(val) >> 3) * 8;
 	char *p;
 
 	if ((*s = lookup_segment((*s)->capn, *s, U32(val >> 32))) == NULL) {
@@ -264,7 +268,7 @@ static uint64_t lookup_double(struct capn_segment **s, char **d, uint64_t val) {
 }
 
 static uint64_t lookup_far(struct capn_segment **s, char **d, uint64_t val) {
-	uint32_t off = (U32(val) >> 3) * 8;
+	size_t off = (U32(val) >> 3) * 8;
 
 	if ((*s = lookup_segment((*s)->capn, *s, U32(val >> 32))) == NULL) {
 		return 0;
@@ -369,7 +373,7 @@ static capn_ptr read_ptr(struct capn_segment *s, char *d) {
 			e = d + ret.len * 8;
 			break;
 		case COMPOSITE_LIST:
-			if (d+8-s->data > s->len) {
+			if ((size_t)((d+8) - s->data) > s->len) {
 				goto err;
 			}
 
@@ -394,7 +398,7 @@ static capn_ptr read_ptr(struct capn_segment *s, char *d) {
 		goto err;
 	}
 
-	if (e - s->data > s->len)
+	if ((size_t)(e - s->data) > s->len)
 		goto err;
 
 	ret.data = d;
@@ -664,7 +668,7 @@ static int copy_ptr(struct capn_segment *seg, char *data, struct capn_ptr *t, st
 		struct capn_segment *cs = c->copylist;
 
 		/* need to allocate a struct copy */
-		if (!cs || cs->len + sizeof(*n) > cs->cap) {
+		if (!cs || cs->len + (int)sizeof(*n) > cs->cap) {
 			cs = c->create_local ? c->create_local(c->user, sizeof(*n)) : NULL;
 			if (!cs) {
 				/* can't allocate a copy structure */
diff --git a/capn.h b/capn.h
index 26050a1..2af882d 100644
--- a/capn.h
+++ b/capn.h
@@ -94,7 +94,7 @@ struct capn_segment {
 	uint32_t id;
 	/* user settable */
 	char *data;
-	unsigned len, cap;
+	size_t len, cap;
 	void *user;
 };
 
@@ -262,9 +262,9 @@ void capn_reset_copy(struct capn *c);
  */
 struct capn_stream {
 	const uint8_t *next_in;
-	unsigned avail_in;
+	size_t avail_in;
 	uint8_t *next_out;
-	unsigned avail_out;
+	size_t avail_out;
 	unsigned zeros, raw;
 };
 
diff --git a/compiler/capnpc-c.c b/compiler/capnpc-c.c
index c8675a4..42f0d3a 100644
--- a/compiler/capnpc-c.c
+++ b/compiler/capnpc-c.c
@@ -930,7 +930,7 @@ static void define_struct(struct node *n) {
 }
 
 #if 0
-Commenting out interfaces until the RPC protocol has been specified
+/* Commenting out interfaces until the RPC protocol has been spec'd */
 static int find_offset(struct str *v, int inc, uint64_t mask) {
 	int i, j;
 	union {uint64_t u; char c[8];} umask;
@@ -1248,7 +1248,7 @@ int main() {
 			fprintf(srcf, "static const capn_ptr capn_null = {CAPN_NULL};\n");
 
 		if (g_valseg.len > 8) {
-			fprintf(srcf, "static const uint8_t capn_buf[%d] = {", g_valseg.len-8);
+			fprintf(srcf, "static const uint8_t capn_buf[%lu] = {", g_valseg.len-8);
 			for (j = 8; j < g_valseg.len; j++) {
 				if (j > 8)
 					fprintf(srcf, ",");
@@ -1258,7 +1258,7 @@ int main() {
 			}
 			fprintf(srcf, "\n};\n");
 
-			fprintf(srcf, "static const struct capn_segment capn_seg = {{0},0,0,0,(char*)&capn_buf[0],%d,%d};\n",
+			fprintf(srcf, "static const struct capn_segment capn_seg = {{0},0,0,0,(char*)&capn_buf[0],%lu,%lu};\n",
 					g_valseg.len-8, g_valseg.len-8);
 		}