diff --git a/driver-bitforce.c b/driver-bitforce.c
index 0f2ea658..5b8570eb 100644
--- a/driver-bitforce.c
+++ b/driver-bitforce.c
@@ -146,13 +146,13 @@ static bool bitforce_detect_one(const char *devpath)
 } while(0)
 
 #ifdef WIN32
-static char bitforce_autodetect_ftdi(void)
+static int bitforce_autodetect_ftdi(void)
 {
 	char buf[65 * numDevs];
 	char*bufptrs[numDevs + 1];
 	char devpath[] = "\\\\.\\COMnnnnn";
 	char *devpathnum = &devpath[7];
-	char found = 0;
+	int found = 0;
 	int i;
 
 	FT_STATUS ftStatus;
@@ -210,13 +210,13 @@ out:
 	return found;
 }
 #else
-static char bitforce_autodetect_ftdi(void)
+static int bitforce_autodetect_ftdi(void)
 {
 	return 0;
 }
 #endif
 
-static char bitforce_detect_auto(void)
+static int bitforce_detect_auto(void)
 {
 	return (serial_autodetect_udev     (bitforce_detect_one, "BitFORCE*SHA256") ?:
 		serial_autodetect_devserial(bitforce_detect_one, "BitFORCE_SHA256") ?:
diff --git a/driver-modminer.c b/driver-modminer.c
index ff96ee45..040100db 100644
--- a/driver-modminer.c
+++ b/driver-modminer.c
@@ -91,7 +91,7 @@ modminer_detect_one(const char *devpath)
 
 #undef bailout
 
-static char
+static int
 modminer_detect_auto()
 {
 	return
diff --git a/fpgautils.c b/fpgautils.c
index 5f488740..a62b4913 100644
--- a/fpgautils.c
+++ b/fpgautils.c
@@ -38,7 +38,7 @@
 #include "miner.h"
 
 #ifdef HAVE_LIBUDEV
-char
+int
 serial_autodetect_udev(detectone_func_t detectone, const char*prodname)
 {
 	struct udev *udev = udev_new();
@@ -69,14 +69,14 @@ serial_autodetect_udev(detectone_func_t detectone, const char*prodname)
 	return found;
 }
 #else
-char
+int
 serial_autodetect_udev(__maybe_unused detectone_func_t detectone, __maybe_unused const char*prodname)
 {
 	return 0;
 }
 #endif
 
-char
+int
 serial_autodetect_devserial(detectone_func_t detectone, const char*prodname)
 {
 #ifndef WIN32
@@ -107,7 +107,7 @@ serial_autodetect_devserial(detectone_func_t detectone, const char*prodname)
 #endif
 }
 
-char
+int
 _serial_detect(const char*dname, detectone_func_t detectone, autoscan_func_t autoscan, bool forceauto)
 {
 	struct string_elist *iter, *tmp;
diff --git a/fpgautils.h b/fpgautils.h
index c45183b7..5b743bc5 100644
--- a/fpgautils.h
+++ b/fpgautils.h
@@ -14,17 +14,17 @@
 #include <stdio.h>
 
 typedef bool(*detectone_func_t)(const char*);
-typedef char(*autoscan_func_t)();
+typedef int(*autoscan_func_t)();
 
-extern char _serial_detect(const char*dname, detectone_func_t, autoscan_func_t, bool force_autoscan);
+extern int _serial_detect(const char*dname, detectone_func_t, autoscan_func_t, bool force_autoscan);
 #define serial_detect_fauto(dname, detectone, autoscan)  \
 	_serial_detect(dname, detectone, autoscan, true)
 #define serial_detect_auto(dname, detectone, autoscan)  \
 	_serial_detect(dname, detectone, autoscan, false)
 #define serial_detect(dname, detectone)  \
 	_serial_detect(dname, detectone,     NULL, false)
-extern char serial_autodetect_devserial(detectone_func_t, const char*prodname);
-extern char serial_autodetect_udev     (detectone_func_t, const char*prodname);
+extern int serial_autodetect_devserial(detectone_func_t, const char*prodname);
+extern int serial_autodetect_udev     (detectone_func_t, const char*prodname);
 
 extern int serial_open(const char*devpath, unsigned long baud, signed short timeout, bool purge);
 extern ssize_t _serial_read(int fd, char *buf, size_t buflen, char*eol);