diff --git a/arch/arm/cpu/tegra114-common/clock.c b/arch/arm/cpu/tegra114-common/clock.c
index 47612e12d2..3bede71a7a 100644
--- a/arch/arm/cpu/tegra114-common/clock.c
+++ b/arch/arm/cpu/tegra114-common/clock.c
@@ -103,7 +103,7 @@ static enum clock_id clock_source[CLOCK_TYPE_COUNT][CLOCK_MAX_MUX+1] = {
 		MASK_BITS_31_29},
 	{ CLK(PERIPH),	CLK(CGENERAL),	CLK(SFROM32KHZ),	CLK(OSC),
 		CLK(NONE),	CLK(NONE),	CLK(NONE),	CLK(NONE),
-		MASK_BITS_29_28}
+		MASK_BITS_31_28}
 };
 
 /*
diff --git a/arch/arm/cpu/tegra30-common/clock.c b/arch/arm/cpu/tegra30-common/clock.c
index 89c3529c88..3352870218 100644
--- a/arch/arm/cpu/tegra30-common/clock.c
+++ b/arch/arm/cpu/tegra30-common/clock.c
@@ -102,7 +102,7 @@ static enum clock_id clock_source[CLOCK_TYPE_COUNT][CLOCK_MAX_MUX+1] = {
 		MASK_BITS_31_29},
 	{ CLK(PERIPH),  CLK(CGENERAL),  CLK(SFROM32KHZ), CLK(OSC),
 		CLK(NONE),      CLK(NONE),      CLK(NONE),      CLK(NONE),
-		MASK_BITS_29_28}
+		MASK_BITS_31_28}
 };
 
 /*
diff --git a/arch/arm/include/asm/arch-tegra/clock.h b/arch/arm/include/asm/arch-tegra/clock.h
index 052c0208b1..80825e30f8 100644
--- a/arch/arm/include/asm/arch-tegra/clock.h
+++ b/arch/arm/include/asm/arch-tegra/clock.h
@@ -20,10 +20,19 @@ enum clock_osc_freq {
 	CLOCK_OSC_FREQ_COUNT,
 };
 
+/*
+ * Note that no Tegra clock register actually uses all of bits 31:28 as
+ * the mux field. Rather, bits 30:28, 29:28, or 28 are used. However, in
+ * those cases, nothing is stored in the bits about the mux field, so it's
+ * safe to pretend that the mux field extends all the way to the end of the
+ * register. As such, the U-Boot clock driver is currently a bit lazy, and
+ * doesn't distinguish between 31:28, 30:28, 29:28 and 28; it just lumps
+ * them all together and pretends they're all 31:28.
+ */
 enum {
 	MASK_BITS_31_30	= 2,	/* num of bits used to specify clock source */
 	MASK_BITS_31_29,
-	MASK_BITS_29_28,
+	MASK_BITS_31_28,
 };
 
 #include <asm/arch/clock-tables.h>