diff --git a/hw/xfree86/common/xf86.h b/hw/xfree86/common/xf86.h
index 37ac42c5e..143be1e46 100644
--- a/hw/xfree86/common/xf86.h
+++ b/hw/xfree86/common/xf86.h
@@ -389,7 +389,7 @@ extern _X_EXPORT ModeStatus
 xf86CheckModeForDriver(ScrnInfoPtr scrp, DisplayModePtr mode, int flags);
 extern _X_EXPORT int
 xf86ValidateModes(ScrnInfoPtr scrp, DisplayModePtr availModes,
-                  char **modeNames, ClockRangePtr clockRanges,
+                  const char **modeNames, ClockRangePtr clockRanges,
                   int *linePitches, int minPitch, int maxPitch,
                   int minHeight, int maxHeight, int pitchInc,
                   int virtualX, int virtualY, int apertureSize,
diff --git a/hw/xfree86/common/xf86Mode.c b/hw/xfree86/common/xf86Mode.c
index 15214eab8..44bc55953 100644
--- a/hw/xfree86/common/xf86Mode.c
+++ b/hw/xfree86/common/xf86Mode.c
@@ -1354,7 +1354,7 @@ scanLineWidth(unsigned int xsize,       /* pixels */
 
 int
 xf86ValidateModes(ScrnInfoPtr scrp, DisplayModePtr availModes,
-                  char **modeNames, ClockRangePtr clockRanges,
+                  const char **modeNames, ClockRangePtr clockRanges,
                   int *linePitches, int minPitch, int maxPitch, int pitchInc,
                   int minHeight, int maxHeight, int virtualX, int virtualY,
                   int apertureSize, LookupModeFlags strategy)