diff --git a/sys/gdb/gdb_int.h b/sys/gdb/gdb_int.h
index 9ef83d707be2..54defe4af7d2 100644
--- a/sys/gdb/gdb_int.h
+++ b/sys/gdb/gdb_int.h
@@ -31,6 +31,10 @@
 #ifndef _GDB_GDB_INT_H_
 #define	_GDB_GDB_INT_H_
 
+#ifndef EOF
+#define EOF	(-1)
+#endif
+
 extern struct gdb_dbgport *gdb_cur;
 
 extern int gdb_listening;
@@ -54,7 +58,7 @@ gdb_rx_char(void)
 		c = *gdb_rxp++;
 		gdb_rxsz--;
 	} else
-		c = -1;
+		c = EOF;
 	return (c);
 }
 
diff --git a/sys/gdb/gdb_main.c b/sys/gdb/gdb_main.c
index 6d92291b6a19..a7e53c67fb95 100644
--- a/sys/gdb/gdb_main.c
+++ b/sys/gdb/gdb_main.c
@@ -653,7 +653,10 @@ gdb_trap(int type, int code)
 		case 'H': {	/* Set thread. */
 			intmax_t tid;
 			struct thread *thr;
-			gdb_rx_char();
+
+			/* Ignore 'g' (general) or 'c' (continue) flag. */
+			(void) gdb_rx_char();
+
 			if (gdb_rx_varhex(&tid)) {
 				gdb_tx_err(EINVAL);
 				break;
@@ -768,7 +771,7 @@ gdb_trap(int type, int code)
 				gdb_tx_err(ENOENT);
 			break;
 		}
-		case -1:
+		case EOF:
 			/* Empty command. Treat as unknown command. */
 			/* FALLTHROUGH */
 		default:
diff --git a/sys/gdb/gdb_packet.c b/sys/gdb/gdb_packet.c
index 73a431830258..2a8f982ba49c 100644
--- a/sys/gdb/gdb_packet.c
+++ b/sys/gdb/gdb_packet.c
@@ -197,7 +197,7 @@ gdb_rx_varhex(uintmax_t *vp)
 		v += C2N(c);
 		c = gdb_rx_char();
 	} while (isxdigit(c));
-	if (c != -1) {
+	if (c != EOF) {
 		gdb_rxp--;
 		gdb_rxsz++;
 	}
@@ -343,13 +343,12 @@ gdb_rx_bindata(unsigned char *data, size_t datalen, size_t *amt)
 
 	while (*amt < datalen) {
 		c = gdb_rx_char();
-		/* End of packet? */
-		if (c == -1)
+		if (c == EOF)
 			break;
 		/* Escaped character up next */
 		if (c == '}') {
-			/* Truncated packet? Bail out */
-			if ((c = gdb_rx_char()) == -1)
+			/* Malformed packet. */
+			if ((c = gdb_rx_char()) == EOF)
 				return (1);
 			c ^= 0x20;
 		}