diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index c50637d..e4bceba 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -312,6 +312,7 @@ unsigned long tpm_calc_ordinal_duration(struct tpm_chip *chip,
 	int duration = 0;
 	u8 category = (ordinal >> 24) & 0xFF;
 
+	ordinal &= 0xFFFF; /* command ordinal index - low 16 bits */
 	if ((category == TPM_PROTECTED_COMMAND && ordinal < TPM_MAX_ORDINAL) ||
 	    (category == TPM_CONNECTION_COMMAND && ordinal < TSC_MAX_ORDINAL))
 		duration_idx = tpm_ordinal_duration[ordinal];