diff --git a/src/client.c b/src/client.c
index e2ac39e..5d67c43 100644
--- a/src/client.c
+++ b/src/client.c
@@ -152,7 +152,7 @@ immediate_mode_defaults()
 #ifdef DEBUG_BUILD
 #define QTRACK_DEBUG(l, ...) \
 	if (this.debug >= l) {\
-		TIMEPRINT("[QTRACK (%lu/%lu), ? %lu, TO %lu, S %lu/%lu] ", this.num_pending, PENDING_QUERIES_LENGTH, \
+		TIMEPRINT("[QTRACK (%" L "u/%" L "u), ? %" L "u, TO %" L "u, S %" L "u/%" L "u] ", this.num_pending, PENDING_QUERIES_LENGTH, \
 				this.num_untracked, this.num_timeouts, window_sending(this.outbuf, NULL), this.outbuf->numitems); \
 		fprintf(stderr, __VA_ARGS__);\
 		fprintf(stderr, "\n");\
@@ -333,7 +333,7 @@ send_query(uint8_t *hostname)
 	struct query q;
 	size_t len;
 
-	DEBUG(3, "TX: pkt len %lu: hostname '%s'", strlen((char *)hostname), hostname);
+	DEBUG(3, "TX: pkt len %" L "u: hostname '%s'", strlen((char *)hostname), hostname);
 
 	this.chunkid += 7727;
 	if (this.chunkid == 0)
@@ -529,7 +529,7 @@ send_next_frag()
 	if (datacmc >= 36)
 		datacmc = 0;
 
-	DEBUG(3, " SEND DATA: seq %d, ack %d, len %lu, s%d e%d c%d flags %1X",
+	DEBUG(3, " SEND DATA: seq %d, ack %d, len %" L "u, s%d e%d c%d flags %1X",
 			f->seqID, f->ack_other, f->len, f->start, f->end, f->compressed, hdr[2] >> 4);
 
 	id = send_query(buf);
@@ -910,7 +910,7 @@ parse_data(uint8_t *data, size_t len, fragment *f, int *immediate)
 		up_wsize = data[4];
 		dn_start_seq = data[5];
 		up_start_seq = data[6];
-		DEBUG(3, "PING pkt data=%lu WS: up=%u, dn=%u; Start: up=%u, dn=%u",
+		DEBUG(3, "PING pkt data=%" L "u WS: up=%u, dn=%u; Start: up=%u, dn=%u",
 					len - headerlen, up_wsize, dn_wsize, up_start_seq, dn_start_seq);
 	}
 	f->len = len - headerlen;
@@ -931,7 +931,7 @@ tunnel_tun()
 	if ((read = read_tun(this.tun_fd, in, sizeof(in))) <= 0)
 		return -1;
 
-	DEBUG(2, " IN: %lu bytes on tunnel, to be compressed: %d", read, this.compression_up);
+	DEBUG(2, " IN: %" L "u bytes on tunnel, to be compressed: %d", read, this.compression_up);
 
 	if (this.conn != CONN_DNS_NULL || this.compression_up) {
 		datalen = sizeof(out);
@@ -945,7 +945,7 @@ tunnel_tun()
 	if (this.conn == CONN_DNS_NULL) {
 		/* Check if outgoing buffer can hold data */
 		if (window_buffer_available(this.outbuf) < (read / MAX_FRAGSIZE) + 1) {
-			DEBUG(1, "  Outgoing buffer full (%lu/%lu), not adding data!",
+			DEBUG(1, "  Outgoing buffer full (%" L "u/%" L "u), not adding data!",
 						this.outbuf->numitems, this.outbuf->length);
 			return -1;
 		}
@@ -1002,14 +1002,14 @@ tunnel_dns()
 			if (this.lazymode) {
 
 				if (this.send_query_recvcnt < 500 && this.num_servfail < 4) {
-					fprintf(stderr, "Hmm, that's %ld SERVFAILs. Your data should still go through...\n", this.num_servfail);
+					fprintf(stderr, "Hmm, that's %" L "d SERVFAILs. Your data should still go through...\n", this.num_servfail);
 
 				} else if (this.send_query_recvcnt < 500 && this.num_servfail >= 10 &&
 					this.autodetect_server_timeout && this.max_timeout_ms >= 500 && this.num_servfail % 5 == 0) {
 
 					this.max_timeout_ms -= 200;
 					double target_timeout = (float) this.max_timeout_ms / 1000.0;
-					fprintf(stderr, "Too many SERVFAILs (%ld), reducing timeout to"
+					fprintf(stderr, "Too many SERVFAILs (%" L "d), reducing timeout to"
 						" %.1f secs. (use -I%.1f next time on this network)\n",
 							this.num_servfail, target_timeout, target_timeout);
 
@@ -1041,7 +1041,7 @@ tunnel_dns()
 	if (read == 5 && !strncmp("BADIP", (char *)cbuf, 5)) {
 		this.num_badip++;
 		if (this.num_badip % 5 == 1) {
-			fprintf(stderr, "BADIP (%ld): Server rejected sender IP address (maybe iodined -c will help), or server "
+			fprintf(stderr, "BADIP (%" L "d): Server rejected sender IP address (maybe iodined -c will help), or server "
 					"kicked us due to timeout. Will exit if no downstream data is received in 60 seconds.\n", this.num_badip);
 		}
 		return -1;	/* nothing done */
@@ -1059,7 +1059,7 @@ tunnel_dns()
 	got_response(q.id, immediate, 0);
 
 	if ((this.debug >= 3 && res) || (this.debug >= 2 && !res))
-		fprintf(stderr, " RX %s; frag ID %3u, ACK %3d, compression %d, datalen %lu, s%d e%d\n",
+		fprintf(stderr, " RX %s; frag ID %3u, ACK %3d, compression %d, datalen %" L "u, s%d e%d\n",
 				res ? "PING" : "DATA", f.seqID, f.ack_other, f.compressed, f.len, f.start, f.end);
 
 
@@ -1100,7 +1100,7 @@ tunnel_dns()
 		if (compressed) {
 			buflen = sizeof(buf);
 			if ((res = uncompress(buf, &buflen, cbuf, datalen)) != Z_OK) {
-				DEBUG(1, "Uncompress failed (%d) for data len %lu: reassembled data corrupted or incomplete!", res, datalen);
+				DEBUG(1, "Uncompress failed (%d) for data len %" L "u: reassembled data corrupted or incomplete!", res, datalen);
 				datalen = 0;
 			} else {
 				datalen = buflen;
@@ -1189,7 +1189,7 @@ client_tunnel()
 
 				sending--;
 				total--;
-				QTRACK_DEBUG(3, "Sent a query to fill server lazy buffer to %lu, will send another %d",
+				QTRACK_DEBUG(3, "Sent a query to fill server lazy buffer to %" L "u, will send another %d",
 							 this.lazymode ? this.windowsize_down : 1, total);
 
 				if (sending > 0 || (total > 0 && this.lazymode)) {
@@ -2409,7 +2409,7 @@ handshake_set_timeout()
 	char in[4096];
 	int read, id;
 
-	fprintf(stderr, "Setting window sizes to %lu frags upstream, %lu frags downstream...\n",
+	fprintf(stderr, "Setting window sizes to %" L "u frags upstream, %" L "u frags downstream...\n",
 		this.windowsize_up, this.windowsize_down);
 
 	fprintf(stderr, "Calculating round-trip time...");
diff --git a/src/common.h b/src/common.h
index 44266ad..56c6078 100644
--- a/src/common.h
+++ b/src/common.h
@@ -45,6 +45,32 @@ extern const unsigned char raw_header[RAW_HDR_LEN];
 
 #define DNS_PORT 53
 
+#if _WIN32 || _WIN64
+#if _WIN64
+#define BITS_64
+#else
+#define BITS_32
+#endif
+#endif
+
+#if __GNUC__
+#if __x86_64__ || __ppc64__
+#define BITS_64 1
+#else
+#define BITS_32 1
+#endif
+#endif
+
+/* Determine appropriate format specifier for long int on 32/64 bit systems */
+#if BITS_64
+#define FMT_LONG "l"
+#else
+#define FMT_LONG ""
+#endif
+
+/* For convenience and shortness */
+#define L FMT_LONG
+
 #ifndef MIN
 #define MIN(a,b) ((a)<(b)?(a):(b))
 #endif
diff --git a/src/server.c b/src/server.c
index a4040c9..3d6161b 100644
--- a/src/server.c
+++ b/src/server.c
@@ -103,7 +103,7 @@ send_raw(int fd, uint8_t *buf, size_t buflen, int user, int cmd, struct sockaddr
 
 #define QMEM_DEBUG(l, u, ...) \
 	if (server.debug >= l) {\
-		TIMEPRINT("[QMEM u%d (%lu/%u)] ", u, users[u].qmem.num_pending, users[u].outgoing->windowsize); \
+		TIMEPRINT("[QMEM u%d (%" L "u/%u)] ", u, users[u].qmem.num_pending, users[u].outgoing->windowsize); \
 		fprintf(stderr, __VA_ARGS__);\
 		fprintf(stderr, "\n");\
 	}
@@ -184,7 +184,7 @@ qmem_append(int userid, struct query *q)
 		buf->start = (buf->start + 1) % QMEM_LEN;
 	}
 
-	QMEM_DEBUG(5, userid, "add query ID %d, timeout %lu ms", q->id, timeval_to_ms(&users[userid].dns_timeout));
+	QMEM_DEBUG(5, userid, "add query ID %d, timeout %" L "u ms", q->id, timeval_to_ms(&users[userid].dns_timeout));
 
 	/* Copy query into buffer */
 	memcpy(&buf->queries[buf->end].q, q, sizeof(struct query));
@@ -314,7 +314,7 @@ qmem_max_wait(int *touser, struct query **sendq)
 						q->id, age_ms, immediate ? "immediate" : "lazy", timeval_to_ms(&u->dns_timeout));
 
 				sent++;
-				QMEM_DEBUG(4, userid, "ANSWER q id %d, ACK %d; sent %lu of %lu + sending another %lu",
+				QMEM_DEBUG(4, userid, "ANSWER q id %d, ACK %d; sent %" L "u of %" L "u + sending another %" L "u",
 						q->id, u->next_upstream_ack, sent, total, sending);
 
 				send_data_or_ping(userid, q, 0, immediate);
@@ -339,7 +339,7 @@ qmem_max_wait(int *touser, struct query **sendq)
 	if (server.debug >= 5) {
 		time_t soonest_ms = timeval_to_ms(&soonest);
 		if (nextq && nextuser >= 0) {
-			QMEM_DEBUG(5, nextuser, "can wait for %lu ms, will send id %d", soonest_ms, nextq->id);
+			QMEM_DEBUG(5, nextuser, "can wait for %" L "u ms, will send id %d", soonest_ms, nextq->id);
 		} else {
 			if (nextuser < 0)
 				nextuser = 0;
@@ -347,7 +347,7 @@ qmem_max_wait(int *touser, struct query **sendq)
 				/* only if resending some frags */
 				QMEM_DEBUG(5, nextuser, "Resending some fragments")
 			} else {
-				QMEM_DEBUG(2, nextuser, "Don't need to send anything to any users, waiting %lu ms", soonest_ms);
+				QMEM_DEBUG(2, nextuser, "Don't need to send anything to any users, waiting %" L "u ms", soonest_ms);
 			}
 		}
 	}
@@ -479,7 +479,7 @@ send_data_or_ping(int userid, struct query *q, int ping, int immediate)
 	if (datalen + headerlen > sizeof(pkt)) {
 		/* Should never happen, or at least user should be warned about
 		 * fragsize > MAX_FRAGLEN earlier on */
-		warnx("send_frag_or_dataless: fragment too large to send! (%lu)", datalen);
+		warnx("send_frag_or_dataless: fragment too large to send! (%" L "u)", datalen);
 		return;
 	}
 	if (f)
@@ -535,7 +535,7 @@ user_send_data(int userid, uint8_t *indata, size_t len, int compressed)
 		datalen = sizeof(out);
 		ret = uncompress(out, &datalen, indata, len);
 		if (ret != Z_OK) {
-			DEBUG(1, "FAIL: Uncompress == %d: %lu bytes to user %d!", ret, len, userid);
+			DEBUG(1, "FAIL: Uncompress == %d: %" L "u bytes to user %d!", ret, len, userid);
 			return 0;
 		}
 	}
@@ -800,7 +800,7 @@ handle_full_packet(int userid, uint8_t *data, size_t len, int compressed)
 	if (ret == Z_OK) {
 		hdr = (struct ip*) (out + 4);
 		touser = find_user_by_ip(hdr->ip_dst.s_addr);
-		DEBUG(2, "FULL PKT: %lu bytes from user %d (touser %d)", len, userid, touser);
+		DEBUG(2, "FULL PKT: %" L "u bytes from user %d (touser %d)", len, userid, touser);
 		if (touser == -1) {
 			/* send the uncompressed packet to tun device */
 			write_tun(server.tun_fd, rawdata, rawlen);
@@ -823,7 +823,7 @@ handle_raw_login(uint8_t *packet, size_t len, struct query *q, int fd, int useri
 	char myhash[16];
 
 	if (len < 16) {
-		DEBUG(2, "Invalid raw login packet: length %lu < 16 bytes!", len);
+		DEBUG(2, "Invalid raw login packet: length %" L "u < 16 bytes!", len);
 		return;
 	}
 
@@ -833,7 +833,7 @@ handle_raw_login(uint8_t *packet, size_t len, struct query *q, int fd, int useri
 		return;
 	}
 
-	DEBUG(1, "RX-raw: login, len %lu, from user %d", len, userid);
+	DEBUG(1, "RX-raw: login, len %" L "u, from user %d", len, userid);
 
 	/* User sends hash of seed + 1 */
 	login_calculate(myhash, 16, server.password, users[userid].seed + 1);
@@ -867,7 +867,7 @@ handle_raw_data(uint8_t *packet, size_t len, struct query *q, int userid)
 
 	/* copy to packet buffer, update length */
 
-	DEBUG(3, "RX-raw: full pkt raw, length %lu, from user %d", len, userid);
+	DEBUG(3, "RX-raw: full pkt raw, length %" L "u, from user %d", len, userid);
 
 	handle_full_packet(userid, packet, len, 1);
 }
@@ -904,7 +904,7 @@ raw_decode(uint8_t *packet, size_t len, struct query *q, int dns_fd)
 	raw_cmd = RAW_HDR_GET_CMD(packet);
 	raw_user = RAW_HDR_GET_USR(packet);
 
-	DEBUG(3, "RX-raw: client %s, user %d, raw command 0x%02X, length %lu",
+	DEBUG(3, "RX-raw: client %s, user %d, raw command 0x%02X, length %" L "u",
 			  format_addr(&q->from, q->fromlen), raw_user, raw_cmd, len);
 
 	packet += RAW_HDR_LEN;
@@ -1122,7 +1122,7 @@ write_dns(int fd, struct query *q, char *data, size_t datalen, char downenc)
 		return;
 	}
 
-	DEBUG(3, "TX: client %s ID %5d, %lu bytes data, type %d, name '%10s'",
+	DEBUG(3, "TX: client %s ID %5d, %" L "u bytes data, type %d, name '%10s'",
 			format_addr(&q->from, q->fromlen), q->id, datalen, q->type, q->name);
 
 	sendto(fd, buf, len, 0, (struct sockaddr*)&q->from, q->fromlen);
@@ -1149,7 +1149,7 @@ handle_null_request(int dns_fd, struct query *q, int domain_len)
 
 	memcpy(in, q->name, MIN(domain_len, sizeof(in)));
 
-	DEBUG(3, "NULL request length %d/%lu, command '%c'", domain_len, sizeof(in), in[0]);
+	DEBUG(3, "NULL request length %d/%" L "u, command '%c'", domain_len, sizeof(in), in[0]);
 
 	if(in[0] == 'V' || in[0] == 'v') { /* Version request */
 		uint32_t version = !PROTOCOL_VERSION;
@@ -1544,7 +1544,7 @@ handle_null_request(int dns_fd, struct query *q, int domain_len)
 
 		read = unpack_data(unpacked, sizeof(unpacked), in + 1, domain_len - 1, b32);
 		if (read < UPSTREAM_PING) {
-			DEBUG(1, "Invalid ping! Length %lu", read);
+			DEBUG(1, "Invalid ping! Length %" L "u", read);
 			return;
 		}
 
diff --git a/src/window.c b/src/window.c
index 72a0ad5..3fe3c09 100644
--- a/src/window.c
+++ b/src/window.c
@@ -155,7 +155,7 @@ window_process_incoming_fragment(struct frag_buffer *w, fragment *f)
 	}
 	/* Place fragment into correct location in buffer */
 	ssize_t dest = WRAP(w->window_start + SEQ_OFFSET(startid, f->seqID));
-	WDEBUG("   Putting frag seq %u into frags[%lu + %u = %lu]",
+	WDEBUG("   Putting frag seq %u into frags[%" L "u + %u = %" L "u]",
 		   f->seqID, w->window_start, SEQ_OFFSET(startid, f->seqID), dest);
 
 	/* Check if fragment already received */
@@ -192,7 +192,7 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 	if (w->direction != WINDOW_RECVING)
 		return 0;
 	if (w->frags[w->chunk_start].start == 0 && w->numitems > 0) {
-		WDEBUG("chunk_start (%lu) pointing to non-start fragment (seq %u, len %lu)!",
+		WDEBUG("chunk_start (%" L "u) pointing to non-start fragment (seq %u, len %" L "u)!",
 			  w->chunk_start, w->frags[w->chunk_start].seqID, w->frags[w->chunk_start].len);
 		return 0;
 	}
@@ -208,12 +208,12 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 		f = &w->frags[woffs];
 		fraglen = f->len;
 		if (fraglen == 0 || f->seqID != curseq) {
-			WDEBUG("Missing next frag %u [%lu], got seq %u (%lu bytes) instead! Not reassembling!",
+			WDEBUG("Missing next frag %u [%" L "u], got seq %u (%" L "u bytes) instead! Not reassembling!",
 				   curseq, woffs, f->seqID, fraglen);
 			return 0;
 		}
 
-		WDEBUG("   Fragment seq %u, data length %lu, data offset %lu, total len %lu, maxlen %lu",
+		WDEBUG("   Fragment seq %u, data length %" L "u, data offset %" L "u, total len %" L "u, maxlen %" L "u",
 				f->seqID, fraglen, dest - data, datalen, maxlen);
 		memcpy(dest, f->data, MIN(fraglen, maxlen));
 		dest += fraglen;
@@ -225,7 +225,7 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 			}
 		}
 		if (fraglen > maxlen) {
-			WDEBUG("Data buffer too small! Reassembled %lu bytes.", datalen);
+			WDEBUG("Data buffer too small! Reassembled %" L "u bytes.", datalen);
 			return 0;
 		}
 
@@ -233,7 +233,7 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 		window_tick(w);
 
 		if (f->end == 1) {
-			WDEBUG("Found end of chunk! (seqID %u, chunk len %lu, datalen %lu)", f->seqID, i, datalen);
+			WDEBUG("Found end of chunk! (seqID %u, chunk len %" L "u, datalen %" L "u)", f->seqID, i, datalen);
 			end = 1;
 			break;
 		}
@@ -249,7 +249,7 @@ window_reassemble_data(struct frag_buffer *w, uint8_t *data, size_t maxlen, int
 		return 0;
 	}
 
-	WDEBUG("Reassembled %lu bytes from %lu frags; %scompressed!", datalen, i + 1, *compression ? "" : "un");
+	WDEBUG("Reassembled %" L "u bytes from %" L "u frags; %scompressed!", datalen, i + 1, *compression ? "" : "un");
 	/* Clear all used fragments */
 	size_t p;
 	ITER_FORWARD(w->chunk_start, WRAP(w->chunk_start + i + 1), w->length, p,
@@ -340,7 +340,7 @@ window_get_next_sending_fragment(struct frag_buffer *w, int *other_ack)
 		}
 	}
 	if (f)
-		WDEBUG("Not sending any fragments (last frag checked: retries %u, seqid %u, len %lu)",
+		WDEBUG("Not sending any fragments (last frag checked: retries %u, seqid %u, len %" L "u)",
 				f->retries, f->seqID, f->len);
 	return NULL;
 
@@ -383,7 +383,7 @@ window_ack(struct frag_buffer *w, int seqid)
 			if (f->acks > 0)
 				WDEBUG("DUPE ACK: %d ACKs for seqId %u", f->acks, seqid);
 			f->acks ++;
-			WDEBUG("   ACK frag seq %u, ACKs %u, len %lu, s %u e %u", f->seqID, f->acks, f->len, f->start, f->end);
+			WDEBUG("   ACK frag seq %u, ACKs %u, len %" L "u, s %u e %u", f->seqID, f->acks, f->len, f->start, f->end);
 			break;
 		}
 	}
@@ -400,7 +400,7 @@ window_tick(struct frag_buffer *w)
 			unsigned old_start_id = w->start_seq_id;
 #endif
 			w->start_seq_id = (w->start_seq_id + 1) % MAX_SEQ_ID;
-			WDEBUG("moving window forwards; %lu-%lu (%u) to %lu-%lu (%u) len=%lu",
+			WDEBUG("moving window forwards; %" L "u-%" L "u (%u) to %" L "u-%" L "u (%u) len=%" L "u",
 					w->window_start, w->window_end, old_start_id, AFTER(w, 1),
 					AFTER(w, w->windowsize + 1), w->start_seq_id, w->length);
 			if (w->direction == WINDOW_SENDING) {
@@ -429,7 +429,7 @@ window_add_outgoing_data(struct frag_buffer *w, uint8_t *data, size_t len, int c
 	compressed &= 1;
 	size_t offset = 0;
 	static fragment f;
-	WDEBUG("add data len %lu, %lu frags, max fragsize %u", len, n, w->maxfraglen);
+	WDEBUG("add data len %" L "u, %" L "u frags, max fragsize %u", len, n, w->maxfraglen);
 	for (size_t i = 0; i < n; i++) {
 		memset(&f, 0, sizeof(f));
 		f.len = MIN(len - offset, w->maxfraglen);
@@ -441,7 +441,7 @@ window_add_outgoing_data(struct frag_buffer *w, uint8_t *data, size_t len, int c
 		f.ack_other = -1;
 		window_append_fragment(w, &f);
 		w->cur_seq_id = (w->cur_seq_id + 1) % MAX_SEQ_ID;
-		WDEBUG("     fragment len %lu, seqID %u, s %u, end %u, dOffs %lu", f.len, f.seqID, f.start, f.end, offset);
+		WDEBUG("     fragment len %" L "u, seqID %u, s %u, end %u, dOffs %" L "u", f.len, f.seqID, f.start, f.end, offset);
 		offset += f.len;
 	}
 	return n;