diff --git a/chip/lm4/gpio.c b/chip/lm4/gpio.c
index bce2138ca2..50fa9dbce0 100644
--- a/chip/lm4/gpio.c
+++ b/chip/lm4/gpio.c
@@ -58,7 +58,7 @@ void gpio_set_alternate_function(int port, int mask, int func)
 		clock_wait_cycles(3);
 	}
 
-	if (func) {
+	if (func >= 0) {
 		int pctlmask = 0;
 		int i;
 		/* Expand mask from bits to nibbles */
@@ -196,7 +196,7 @@ void gpio_pre_init(void)
 	/* Set all GPIOs to defaults */
 	for (i = 0; i < GPIO_COUNT; i++, g++) {
 		/* Use as GPIO, not alternate function */
-		gpio_set_alternate_function(g->port, g->mask, 0);
+		gpio_set_alternate_function(g->port, g->mask, -1);
 
 		/* Set up GPIO based on flags */
 		gpio_set_flags(i, g->flags);
diff --git a/chip/lm4/onewire.c b/chip/lm4/onewire.c
index 0c795eeedc..d6677bfa55 100644
--- a/chip/lm4/onewire.c
+++ b/chip/lm4/onewire.c
@@ -158,7 +158,7 @@ void onewire_write(int data)
 static void onewire_init(void)
 {
 	/* Configure 1-wire pin as open-drain GPIO */
-	gpio_set_alternate_function(LM4_GPIO_H, ONEWIRE_PIN, 0);
+	gpio_set_alternate_function(LM4_GPIO_H, ONEWIRE_PIN, -1);
 	LM4_GPIO_ODR(LM4_GPIO_H) |= ONEWIRE_PIN;
 }
 DECLARE_HOOK(HOOK_INIT, onewire_init, HOOK_PRIO_DEFAULT);
diff --git a/chip/lm4/spi.c b/chip/lm4/spi.c
index 09a5ec03a8..4607f7460c 100644
--- a/chip/lm4/spi.c
+++ b/chip/lm4/spi.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
+/* Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
@@ -41,7 +41,7 @@ int spi_enable(int enable)
 		gpio_set_flags(GPIO_SPI_CSn, GPIO_HI_Z);
 
 		/* PA2,4,5 normal function (high-Z GPIOs) */
-		gpio_set_alternate_function(LM4_GPIO_A, 0x34, 0);
+		gpio_set_alternate_function(LM4_GPIO_A, 0x34, -1);
 	}
 
 	return EC_SUCCESS;
diff --git a/chip/stm32/gpio-stm32l15x.c b/chip/stm32/gpio-stm32l15x.c
index 72c118cbf5..dbd7af174c 100644
--- a/chip/stm32/gpio-stm32l15x.c
+++ b/chip/stm32/gpio-stm32l15x.c
@@ -118,6 +118,17 @@ void gpio_set_alternate_function(int port, int mask, int func)
 	uint32_t afr;
 	uint32_t moder = STM32_GPIO_MODER_OFF(port);
 
+	if (func < 0) {
+		/* Return to normal GPIO function, defaulting to input. */
+		while (mask) {
+			bit = 31 - __builtin_clz(mask);
+			moder &= ~(0x3 << (bit * 2 + 16));
+			mask &= ~(1 << bit);
+		}
+		STM32_GPIO_MODER_OFF(port) = moder;
+		return;
+	}
+
 	/* Low half of the GPIO bank */
 	half = mask & 0xff;
 	afr = STM32_GPIO_AFRL_OFF(port);
diff --git a/include/gpio.h b/include/gpio.h
index 9dd97cb3aa..fca33231e0 100644
--- a/include/gpio.h
+++ b/include/gpio.h
@@ -133,7 +133,7 @@ int gpio_enable_interrupt(enum gpio_signal signal);
  *
  * @param port		GPIO port to set (LM4_GPIO_*)
  * @param mask		Bitmask of pins on that port to affect
- * @param func		Alternate function; if 0, configures the specified
+ * @param func		Alternate function; if <0, configures the specified
  *			GPIOs for normal GPIO operation.
  */
 void gpio_set_alternate_function(int port, int mask, int func);