diff --git a/arch/powerpc/cpu/mpc8xxx/fdt.c b/arch/powerpc/cpu/mpc8xxx/fdt.c
index 2847094..857adeb 100644
--- a/arch/powerpc/cpu/mpc8xxx/fdt.c
+++ b/arch/powerpc/cpu/mpc8xxx/fdt.c
@@ -167,6 +167,12 @@ void fdt_fixup_dr_usb(void *blob, bd_t *bd)
 				}
 			}
 
+			if (mode_idx < 0 || phy_idx < 0) {
+				printf("ERROR: wrong usb mode/phy"
+					" defined!!\n");
+				return;
+			}
+
 			dr_mode_type = modes[mode_idx];
 			dr_phy_type = phys[phy_idx];