diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6043635e..a0b0e82e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Emulators
+
+- **VIC-20**: the text window is drawn correctly now. The VIC-I emulated the VIC-II's display window registers, so the 22 column window was placed at a garbage offset: the first character column was clipped in half and the screen was shifted 24 pixels to the right. The VIC-I window is fixed at 22x23 characters and centered in the picture; its vertical position still comes from the ROM (the "upper border" register), so NTSC and PAL ROMs both work.
+
 ### Editor and UI
 
 - The IDE now works in Firefox: a synchronous XHR with a `responseType` hangs in Firefox when the response is 1MB or more, so the build worker hung forever on platforms with a big toolchain package (Game Boy, Atari 8-bit, Apple II, ...). The worker now fetches those packages as ArrayBuffers. A worker that dies no longer leaves the IDE spinning: the error is shown and the build stops.
diff --git a/res/vic20/vic20.wasm b/res/vic20/vic20.wasm
index 34d9f1aa..c1603e4c 100755
Binary files a/res/vic20/vic20.wasm and b/res/vic20/vic20.wasm differ
diff --git a/src/machine/vic20.ts b/src/machine/vic20.ts
index 964d14b1..cf78ffec 100644
--- a/src/machine/vic20.ts
+++ b/src/machine/vic20.ts
@@ -15,7 +15,9 @@ export class VIC20_WASMMachine extends BaseWASMMachine implements Machine, Probe
 
   numTotalScanlines = 312;
   cpuCyclesPerLine = 71;
-  videoOffsetBytes = -24 * 4;
+  // the VIC-I draws its 22x23 character window centered in the frame,
+  // so no video offset is needed
+  videoOffsetBytes = 0;
 
   prgstart : number;
   joymask0 = 0;
@@ -27,6 +29,22 @@ export class VIC20_WASMMachine extends BaseWASMMachine implements Machine, Probe
     super.loadBIOS(srcArray);
   }
   async fetchBIOS() {
+    // use the real VIC-20 ROM set (BASIC, character ROM and KERNAL) if it is
+    // available, otherwise fall back to a tiny stub BIOS that only knows how
+    // to start an autostart cartridge
+    try {
+      const resp = await fetch('res/vic20/vic20.bios');
+      if (resp.status == 200) {
+        const bios = new Uint8Array(await resp.arrayBuffer());
+        if (bios.length == 0x5000) {
+          this.allocateBIOS(bios);
+          this.loadBIOS(bios);
+          return;
+        }
+      }
+    } catch (e) {
+      // no ROM set available, use the stub BIOS below
+    }
     let bios = new Uint8Array(20480);
     bios.set(DEFAULT_BIOS, bios.length - DEFAULT_BIOS.length);
     this.allocateBIOS(bios);
diff --git a/test/cli/testvic20.js b/test/cli/testvic20.js
new file mode 100644
index 00000000..c7f0444d
--- /dev/null
+++ b/test/cli/testvic20.js
@@ -0,0 +1,95 @@
+var assert = require('assert');
+var { loadPlatform } = require('../../gen/tools/emutarget.js');
+
+/*
+    A tiny cartridge that programs the VIC-I and draws two characters, so
+    that the text window can be checked.
+
+    The cartridge file has a 2 byte load address, then the cold and warm
+    start vectors, then the "A0CBM" signature; the code is loaded at $A009:
+
+        $A009  A9 1B       LDA #$1B      ; bg color white, border color cyan
+        $A00B  8D 0F 90    STA $900F
+        $A00D  A9 19       LDA #$19      ; upper border = raster line 25
+        $A00F  8D 01 90    STA $9001
+        $A011  A9 F0       LDA #$F0      ; screen pointer A13..A10
+        $A013  8D 05 90    STA $9005
+        $A015  A9 96       LDA #$96      ; screen pointer A9
+        $A017  8D 02 90    STA $9002
+        $A019  A9 00       LDA #$00      ; clear the screen page
+        $A01B  A2 00       LDX #$00
+        $A01D  9D 00 1E    STA $1E00,X
+        $A020  9D 00 1F    STA $1F00,X
+        $A023  E8          INX
+        $A024  D0 F7       BNE $A01D
+        $A026  A9 06       LDA #$06      ; clear the color RAM, blue
+        $A028  A2 00       LDX #$00
+        $A02A  9D 00 96    STA $9600,X
+        $A02D  E8          INX
+        $A02E  E0 28       CPX #$28
+        $A030  D0 F8       BNE $A02A
+        $A032  A9 48       LDA #'H'
+        $A034  8D 00 1E    STA $1E00
+        $A037  A9 49       LDA #'I'
+        $A039  8D 01 1E    STA $1E01
+        $A03C  4C 40 A0    JMP $A040
+        $A03F  00
+        $A040  4C 40 A0    JMP $A040
+*/
+var CART = [
+    0x00, 0xA0, 0x09, 0xA0, 0x09, 0xA0, 0x41, 0x30, 0xC3, 0xC2, 0xCD, 0xA9,
+    0x1B, 0x8D, 0x0F, 0x90, 0xA9, 0x19, 0x8D, 0x01, 0x90, 0xA9, 0xF0, 0x8D,
+    0x05, 0x90, 0xA9, 0x96, 0x8D, 0x02, 0x90, 0xA9, 0x00, 0xA2, 0x00, 0x9D,
+    0x00, 0x1E, 0x9D, 0x00, 0x1F, 0xE8, 0xD0, 0xF7, 0xA9, 0x06, 0xA2, 0x00,
+    0x9D, 0x00, 0x96, 0xE8, 0xE0, 0x28, 0xD0, 0xF8, 0xA9, 0x48, 0x8D, 0x00,
+    0x1E, 0xA9, 0x49, 0x8D, 0x01, 0x1E, 0x4C, 0x40, 0xA0,
+];
+
+var CYAN = 0xFFFFF04D;
+
+describe('VIC-20 video', function () {
+    it('should draw the 22 column text window centered in the frame', async function () {
+        this.timeout(60000);
+        var target = await loadPlatform('vic20');
+        await target.start();
+        var video = target.getVideo();
+        assert.equal(video.width, 232);
+        assert.equal(video.height, 272);
+        // load the cartridge that programs the VIC
+        await target.loadROM(new Uint8Array(CART), 'cart.bin');
+        // run until the cartridge has set up the screen (with a real KERNAL
+        // this takes a moment, with the stub BIOS it is immediate)
+        var color = function () { return -1; };
+        for (var i = 0; i < 300; i++) {
+            target.advanceFrame();
+            video = target.getVideo();
+            var px = video.pixels;
+            color = function (x, y) { return px[y * video.width + x]; };
+            if (color(0, 100) == CYAN) break;
+        }
+        assert.equal(color(0, 100), CYAN, 'the cartridge screen did not appear');
+        // the cartridge sets the colors before the window position, so let
+        // a few more frames pass before the picture is checked
+        for (var i = 0; i < 5; i++) {
+            target.advanceFrame();
+        }
+        video = target.getVideo();
+        var px = video.pixels;
+        color = function (x, y) { return px[y * video.width + x]; };
+        // the text window is 22 columns (176 pixels) wide and centered, so
+        // there are 28 pixels of border color on either side. The pixels
+        // inside the window are the background color or a character, but
+        // never the border color.
+        assert.equal(color(0, 100), CYAN, 'left border');
+        assert.equal(color(27, 100), CYAN, 'left border');
+        assert.notEqual(color(28, 100), CYAN, 'first text column');
+        assert.notEqual(color(203, 100), CYAN, 'last text column');
+        assert.equal(color(204, 100), CYAN, 'right border');
+        assert.equal(color(231, 100), CYAN, 'right border');
+        // the window is 23 rows (184 lines) tall, starting at raster line 25
+        assert.equal(color(100, 25), CYAN, 'above the text window');
+        assert.notEqual(color(100, 26), CYAN, 'first text row');
+        assert.notEqual(color(100, 209), CYAN, 'last text row');
+        assert.equal(color(100, 210), CYAN, 'below the text window');
+    });
+});