diff --git a/clocks/ns.clock/ns.clock.system.s b/clocks/ns.clock/ns.clock.system.s
index c3e2711..f616e3f 100644
--- a/clocks/ns.clock/ns.clock.system.s
+++ b/clocks/ns.clock/ns.clock.system.s
@@ -278,6 +278,7 @@ loop:   lda     driver,y
 driver:
         php
         sei
+        lda     $C00B           ; Ultrawarp bug workaround c/o @bobbimanners
 ld4:    lda     $CFFF           ; self-modified ($CFFF or RDCXROM)
         pha
 st1:    sta     $C300           ; self-modified ($Cn00 or INTCXROM)
diff --git a/clocks/ns.clock/set.datetime.s b/clocks/ns.clock/set.datetime.s
index 26e65ff..73e56e6 100644
--- a/clocks/ns.clock/set.datetime.s
+++ b/clocks/ns.clock/set.datetime.s
@@ -349,6 +349,7 @@ slot:   .byte   0
 driver:
         php
         sei
+        lda     $C00B           ; Ultrawarp bug workaround c/o @bobbimanners
 ld4:    lda     $CFFF           ; self-modified ($CFFF or RDCXROM)
         pha
 st1:    sta     $C300           ; self-modified ($Cn00 or INTCXROM)
@@ -456,6 +457,7 @@ unlock:
 
         php
         sei
+        lda     $C00B           ; Ultrawarp bug workaround c/o @bobbimanners
 ld4:    lda     $CFFF           ; self-modified ($CFFF or RDCXROM)
         pha
 st1:    sta     $C300           ; self-modified ($Cn00 or INTCXROM)