diff --git a/source/rtc.c b/source/rtc.c
index 3463ea1..5f02594 100644
--- a/source/rtc.c
+++ b/source/rtc.c
@@ -143,10 +143,12 @@ static void rtc_cmd_arg(const unsigned int cmd, unsigned int data, unsigned int
     assume(len > 0 && len <= 32);
     rtc_write(data, len);
 
+    int wait = (TIMEOUT_CYCLES_WAIT_AFTER_WRITE_PER_BYTE * 7 + 11 + 6) / 12;
     __asm__ volatile (
-        "L1%=: subs %[wait], #1"  "\n\t"
-        "bne L1%="
-        ::  [wait]"l"(((TIMEOUT_CYCLES_WAIT_AFTER_WRITE_PER_BYTE * len + 7) / 8 + 11 + 6) / 12)
+        "L1%=:"                      "\n\t"
+        "subs  %[wait], %[wait], #1" "\n\t"
+        "bne   L1%="
+        ::  [wait]"r"(wait)
     );
 }
 
@@ -159,10 +161,12 @@ static void rtc_cmd_arg_datetime(unsigned int cmd, __agbabi_datetime_t datetime,
     rtc_write(date, 32);
     rtc_write(time, 24);
 
+    int wait = (TIMEOUT_CYCLES_WAIT_AFTER_WRITE_PER_BYTE * 7 + 11 + 6) / 12;
     __asm__ volatile (
-        "L1%=: subs %[wait], #1"  "\n\t"
-        "bne L1%="
-        ::  [wait]"l"((TIMEOUT_CYCLES_WAIT_AFTER_WRITE_PER_BYTE * 7 + 11 + 6) / 12)
+        "L1%=:"                      "\n\t"
+        "subs  %[wait], %[wait], #1" "\n\t"
+        "bne   L1%="
+        ::  [wait]"r"(wait)
     );
 }