diff --git a/src/dos_m65/filesystem_vfs/fs_vfs_nextdirentry.s b/src/dos_m65/filesystem_vfs/fs_vfs_nextdirentry.s
index f459b304..0e03fff3 100644
--- a/src/dos_m65/filesystem_vfs/fs_vfs_nextdirentry.s
+++ b/src/dos_m65/filesystem_vfs/fs_vfs_nextdirentry.s
@@ -27,9 +27,7 @@ fs_vfs_nextdirentry:
 	ldx SD_DESC                       ; directory descriptor    XXX rename to FS_HVSR_DESC
 	ldy #>MEM_BUF                     ; target page number
 
-	lda #$14                          ; dos_readdir
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_readddir
 
 	+bcc @fail
 
diff --git a/src/dos_m65/filesystem_vfs/fs_vfs_nextfileblock.s b/src/dos_m65/filesystem_vfs/fs_vfs_nextfileblock.s
index e700a6c7..c5cd21ce 100644
--- a/src/dos_m65/filesystem_vfs/fs_vfs_nextfileblock.s
+++ b/src/dos_m65/filesystem_vfs/fs_vfs_nextfileblock.s
@@ -9,9 +9,7 @@ fs_vfs_nextfileblock:
 	; Read chunk of data to SD card buffer
 
 	ldx SD_DESC
-	lda #$1A                           ; dos_readfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_readfile
 
 	; XXX check error code
 
@@ -26,9 +24,7 @@ fs_vfs_nextfileblock:
 	ora SD_ACPTR_LEN+0
 	bne @copy
 
-	lda #$20                           ; dos_closefile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_closefile
 
 	lda #$00
 	sec
@@ -69,9 +65,7 @@ fs_vfs_file_not_found:
 	jsr util_shadow_restore            ; restore MEM_BUF memory content
 
     ldx SD_DESC
-	lda #$16                           ; dos_closedir
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_closedir
 
 	lda #39                            ; file not found error
 	jsr util_status_SD
diff --git a/src/dos_m65/filesystem_vfs/fs_vfs_read_dir.s b/src/dos_m65/filesystem_vfs/fs_vfs_read_dir.s
index 7cba036f..14dec880 100644
--- a/src/dos_m65/filesystem_vfs/fs_vfs_read_dir.s
+++ b/src/dos_m65/filesystem_vfs/fs_vfs_read_dir.s
@@ -8,9 +8,7 @@ fs_vfs_read_dir_open:
 
 	; Open the directory
 
-	lda #$12                          ; dos_opendir
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_opendir
 
 	; XXX handle read errors
 
@@ -105,9 +103,7 @@ fs_vfs_read_dir_blocksfree:
 	; Close the directory within the hypervisor  XXX maybe move it to close routine
 
     ldx SD_DESC
-	lda #$16                          ; dos_closedir
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_closedir
 
 	clc
 	rts
diff --git a/src/dos_m65/filesystem_vfs/fs_vfs_read_file.s b/src/dos_m65/filesystem_vfs/fs_vfs_read_file.s
index 7c019a68..9cc623bc 100644
--- a/src/dos_m65/filesystem_vfs/fs_vfs_read_file.s
+++ b/src/dos_m65/filesystem_vfs/fs_vfs_read_file.s
@@ -50,9 +50,7 @@ fs_vfs_read_file_open:
 
 	jsr util_shadow_restore            ; restore MEM_BUF memory content
 
-	lda #$18                           ; dos_openfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_openfile
 
 	; XXX check error code
 
diff --git a/src/dos_m65/unit_ramdisk/unit_rd_preload.s b/src/dos_m65/unit_ramdisk/unit_rd_preload.s
index 9bf90c13..4322b264 100644
--- a/src/dos_m65/unit_ramdisk/unit_rd_preload.s
+++ b/src/dos_m65/unit_ramdisk/unit_rd_preload.s
@@ -31,18 +31,14 @@ unit_rd_preload:
 
 	ldy #>MEM_BUF
 	ldx #<MEM_BUF
-	lda #$2E                           ; dos_setname
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_setname
 	jsr util_shadow_restore
 
 	+bcc @error_not_found              ; branch if error
 
 	; Try to find the file
 
-	lda #$34                           ; dos_findfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_findfile
 	+bcc @error_not_found              ; branch if file not found
 
 	; Calculate maximum amount of tracks possible to load
@@ -65,9 +61,7 @@ unit_rd_preload:
 
 	; Load the image
 
-	lda #$18                          ; dos_openfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_openfile
 
 	lda #$FF
 	sta RD_MAXTRACK
@@ -91,9 +85,7 @@ unit_rd_preload:
 
 	; Read 512 bytes
 
-	lda #$1A                           ; dos_readfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_readfile
 
 	cpx #$00
 	bne @error_wrong_size_plx          ; file size not multiplicity of 64K
@@ -119,19 +111,13 @@ unit_rd_preload:
 
 	; Make sure this is the end of the file
 
-	lda #$1A                           ; dos_readfile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_readfile
 
 	cpx #$00
 	bne @error_too_large
 	cpy #$00
 	bne @error_too_large
 
-	lda #$20                           ; dos_closefile
-	sta HTRAP00
-	+nop
-
 @load_image_end:
 
 	plx
@@ -142,9 +128,7 @@ unit_rd_preload:
 	cmp #$02
 	bcc @error_wrong_size              ; file too small, at least 128K required
 
-	lda #$20                           ; dos_closefile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_closefile       ; XXX set descriptor
 
 	; End of initialization
 
@@ -187,9 +171,7 @@ unit_rd_preload_err_common:
 
 	sta RD_MSG                         ; set code for startup screen
 
-	lda #$20                           ; dos_closefile
-	sta HTRAP00
-	+nop
+	jsr util_htrap_dos_closefile       ; XXX set descriptor
 
 	; FALLTROUGH
 
diff --git a/src/dos_m65/unit_sdcard/unit_sd_init.s b/src/dos_m65/unit_sdcard/unit_sd_init.s
index 6f79c036..3f4552e9 100644
--- a/src/dos_m65/unit_sdcard/unit_sd_init.s
+++ b/src/dos_m65/unit_sdcard/unit_sd_init.s
@@ -26,14 +26,5 @@ unit_sd_init:
 
 	; Close all the files in the hypervisor, go to root directory
 
-	lda #$22                          ; dos_closeall
-	sta HTRAP00
-	+nop
-
-	lda #$3C                          ; dos_cdrootdir
-	sta HTRAP00
-	+nop
-
-	; End of initialization
-
-	rts
+	jsr util_htrap_dos_closeall
+	jmp util_htrap_dos_cdrootdir
diff --git a/src/dos_m65/utils/util_htrap.s b/src/dos_m65/utils/util_htrap.s
new file mode 100644
index 00000000..fd73953b
--- /dev/null
+++ b/src/dos_m65/utils/util_htrap.s
@@ -0,0 +1,75 @@
+
+; Size-optimized hypervisor interaction code
+
+
+util_htrap_dos_opendir:
+
+	lda #$12
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_readddir:
+
+	lda #$14
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_closedir:
+
+	lda #$16
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_openfile:
+
+	lda #$18
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_closefile:
+
+	lda #$20
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_closeall:
+
+	lda #$22
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_setname:
+
+	lda #$2E
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_findfile:
+
+	lda #$34
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_cdrootdir:
+
+	lda #$3C
+	+skip_2_bytes_trash_nvz
+
+	; FALLTROUGH
+
+util_htrap_dos_readfile:     ; make sure this is the fastest to execute
+
+	lda #$1A
+
+	sta HTRAP00
+	+nop                     ; NOP required by hypervisor
+
+	rts