diff --git a/libsrc/apple2/filedes.s b/libsrc/apple2/filedes.s
index 094783a79..3a480f6a2 100644
--- a/libsrc/apple2/filedes.s
+++ b/libsrc/apple2/filedes.s
@@ -17,16 +17,12 @@ getfd:
         cmp	#MAX_FDS
         bcs	error
 
-        .if	.sizeof(FD) = 4
 
         ; Convert handle to fdtab slot
+        .assert .sizeof(FD) = 4, error
         asl
         asl
 
-        .else
-        .error	"Assertion failed"
-        .endif
-
         ; Check for fdtab slot in use
         tay
         lda	fdtab + FD::REF_NUM,y
@@ -43,7 +39,7 @@ error:  lda	#EINVAL
 
         .data
 
-fdtab:  .if	.sizeof(FD) = 4
+fdtab:  .assert .sizeof(FD) = 4, error
 
         .byte	$80		; STDIN_FILENO ::REF_NUM
         .byte	O_RDONLY	; STDIN_FILENO ::FLAGS
@@ -57,8 +53,4 @@ fdtab:  .if	.sizeof(FD) = 4
         .byte	O_WRONLY	; STDERR_FILENO::FLAGS
         .addr	$0000		; STDERR_FILENO::BUFFER
 
-        .else
-        .error	"Assertion failed"
-        .endif
-
         .res	(MAX_FDS - 3) * .sizeof(FD)
diff --git a/libsrc/apple2/open.s b/libsrc/apple2/open.s
index ca08735a1..d27be5e8b 100644
--- a/libsrc/apple2/open.s
+++ b/libsrc/apple2/open.s
@@ -37,18 +37,13 @@ _open:
 :       lda	fdtab + FD::REF_NUM,y
         beq	found
 
-        .if	.sizeof(FD) = 4
-
         ; Advance to next fdtab slot
+        .assert .sizeof(FD) = 4, error
         iny
         iny
         iny
         iny
 
-        .else
-        .error	"Assertion failed"
-        .endif
-
         ; Check for end of fdtab
         cpy	#MAX_FDS * .sizeof(FD)
         bcc	:-
@@ -107,13 +102,8 @@ found:  tya
         and	#O_CREAT
         beq	open
 
-        .if	MLI::CREATE::PATHNAME = MLI::OPEN::PATHNAME
-
         ; PATHNAME already set
-
-        .else
-        .error	"Assertion failed"
-        .endif
+        .assert MLI::CREATE::PATHNAME = MLI::OPEN::PATHNAME, error
 
         ; Set all other parameters from template
         ldx	#(MLI::CREATE::CREATE_TIME+1) - (MLI::CREATE::PATHNAME+1) - 1
@@ -138,7 +128,7 @@ found:  tya
         beq	open
 
         lda	#$47		; "Duplicate filename"
-        
+
         ; Cleanup name
 oserr2: jsr	popname		; Preserves A
 
@@ -148,7 +138,7 @@ oserr1: ldy	tmp2		; Restore fdtab slot
         pha			; Save oserror code
         jsr	freebuffer
         pla			; Restore oserror code
-        
+
         ; Return oserror
         jmp	oserrexit
 
@@ -200,20 +190,15 @@ open:   ldy	tmp2		; Restore fdtab slot
 done:   lda	tmp1		; Restore fd
         sta	fdtab + FD::REF_NUM,y
 
-        .if	.sizeof(FD) = 4
-
         ; Convert fdtab slot to handle
+        .assert .sizeof(FD) = 4, error
         tya
         lsr
         lsr
 
-        .else
-        .error	"Assertion failed"
-        .endif
-
         ; Cleanup name
         jsr	popname		; Preserves A
-        
+
         ; Return success
         ldx	#$00
         rts
diff --git a/libsrc/apple2/write.s b/libsrc/apple2/write.s
index 59a30b1e8..056140a9a 100644
--- a/libsrc/apple2/write.s
+++ b/libsrc/apple2/write.s
@@ -44,21 +44,13 @@ _write:
         jsr	callmli
         bcs	oserr
 
-        .if	MLI::MARK::REF_NUM = MLI::EOF::REF_NUM
 
         ; REF_NUM already set
+        .assert MLI::MARK::REF_NUM = MLI::EOF::REF_NUM, error
 
-        .else
-        .error	"Assertion failed"
-        .endif
-
-        .if	MLI::MARK::POSITION = MLI::EOF::EOF
 
         ; POSITION already set
-
-        .else
-        .error	"Assertion failed"
-        .endif
+        .assert MLI::MARK::POSITION = MLI::EOF::EOF, error
 
         ; Set file pointer
         lda	#SET_MARK_CALL
@@ -121,3 +113,4 @@ errno:  jmp	errnoexit
 
         ; Return oserror
 oserr:  jmp	oserrexit
+