diff --git a/crates/effects/src/pixel/edges.rs b/crates/effects/src/pixel/edges.rs
index f1c170600..afed97da2 100644
--- a/crates/effects/src/pixel/edges.rs
+++ b/crates/effects/src/pixel/edges.rs
@@ -10,10 +10,15 @@ pub(super) fn glow(px: &mut [[u8; 4]], w: usize, h: usize, width: f64, brightnes
     }
     let src = px.to_vec();
     let signal = |x: isize, y: isize| -> f32 {
-        if x < 0 || y < 0 { return 0.0; }
-        let Some(p) = src.get(y as usize * w + x as usize) else { return 0.0 };
+        // Beyond the raster's edges is transparency (not the next row's first pixel).
+        let (Ok(x), Ok(y)) = (usize::try_from(x), usize::try_from(y)) else { return 0.0 };
+        if x >= w || y >= h {
+            return 0.0;
+        }
+        let Some(p) = src.get(y * w + x) else { return 0.0 };
         let alpha = f32::from(p[3]) / 255.0;
-        let straight = if alpha > 0.0 { [f32::from(p[0]) / 255.0 / alpha, f32::from(p[1]) / 255.0 / alpha, f32::from(p[2]) / 255.0 / alpha] } else { [0.0; 3] };
+        let straight =
+            if alpha > 0.0 { [f32::from(p[0]) / 255.0 / alpha, f32::from(p[1]) / 255.0 / alpha, f32::from(p[2]) / 255.0 / alpha] } else { [0.0; 3] };
         (0.2126 * straight[0] + 0.7152 * straight[1] + 0.0722 * straight[2]) * alpha
     };
     let mut edges = vec![0.0f32; px.len()];
@@ -21,18 +26,39 @@ pub(super) fn glow(px: &mut [[u8; 4]], w: usize, h: usize, width: f64, brightnes
         for x in 0..w {
             let x = x as isize;
             let y = y as isize;
-            let gx = -signal(x - 1, y - 1) + signal(x + 1, y - 1) - 2.0 * signal(x - 1, y) + 2.0 * signal(x + 1, y) - signal(x - 1, y + 1) + signal(x + 1, y + 1);
-            let gy = -signal(x - 1, y - 1) - 2.0 * signal(x, y - 1) - signal(x + 1, y - 1) + signal(x - 1, y + 1) + 2.0 * signal(x, y + 1) + signal(x + 1, y + 1);
-            if let Some(edge) = edges.get_mut(y as usize * w + x as usize) { *edge = gx.hypot(gy).clamp(0.0, 1.0); }
+            let gx = -signal(x - 1, y - 1) + signal(x + 1, y - 1) - 2.0 * signal(x - 1, y) + 2.0 * signal(x + 1, y) - signal(x - 1, y + 1)
+                + signal(x + 1, y + 1);
+            let gy = -signal(x - 1, y - 1) - 2.0 * signal(x, y - 1) - signal(x + 1, y - 1)
+                + signal(x - 1, y + 1)
+                + 2.0 * signal(x, y + 1)
+                + signal(x + 1, y + 1);
+            if let Some(edge) = edges.get_mut(y as usize * w + x as usize) {
+                *edge = gx.hypot(gy).clamp(0.0, 1.0);
+            }
         }
     }
     blur_plane(&mut edges, w, h, smoothness.max(0.0));
-    if width > 0.5 { blur_plane(&mut edges, w, h, width * 0.5); }
+    if width > 0.5 {
+        blur_plane(&mut edges, w, h, width * 0.5);
+    }
     for (out, (original, edge)) in px.iter_mut().zip(src.iter().zip(edges)) {
         let alpha = f32::from(original[3]) / 255.0;
         let glow = (edge * brightness as f32 / 6.0).clamp(0.0, 1.0);
-        let straight = if original[3] > 0 { [f32::from(original[0]) / 255.0 / alpha.max(1e-6), f32::from(original[1]) / 255.0 / alpha.max(1e-6), f32::from(original[2]) / 255.0 / alpha.max(1e-6)] } else { [1.0, 1.0, 1.0] };
+        let straight = if original[3] > 0 {
+            [
+                f32::from(original[0]) / 255.0 / alpha.max(1e-6),
+                f32::from(original[1]) / 255.0 / alpha.max(1e-6),
+                f32::from(original[2]) / 255.0 / alpha.max(1e-6),
+            ]
+        } else {
+            [1.0, 1.0, 1.0]
+        };
         let a = alpha.max(glow);
-        *out = [(straight[0] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8, (straight[1] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8, (straight[2] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8, (a * 255.0).round() as u8];
+        *out = [
+            (straight[0] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8,
+            (straight[1] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8,
+            (straight[2] * glow * a * 255.0).round().clamp(0.0, 255.0) as u8,
+            (a * 255.0).round() as u8,
+        ];
     }
 }
diff --git a/crates/effects/src/pixel/tests.rs b/crates/effects/src/pixel/tests.rs
index 9a0ebe46d..120e7a1c4 100644
--- a/crates/effects/src/pixel/tests.rs
+++ b/crates/effects/src/pixel/tests.rs
@@ -128,7 +128,19 @@ fn glowing_edges_draw_a_bright_outline_and_preserve_premultiplication() {
     let mut out = src.clone();
     fx("stylize.glowingEdges", json!({"edgeWidth": 1, "smoothness": 1, "edgeBrightness": 20})).apply(&mut out, w, h, &space(w, h));
     assert!(at(&out, w, 3, 4)[0] > 0 || at(&out, w, 4, 4)[0] > 0);
-    assert!(out.chunks_exact(4).all(|p| p[0] <= p[3] && p[1] <= p[3] && p[2] <= p[3]));
+    assert!(out.as_chunks::<4>().0.iter().all(|p| p[0] <= p[3] && p[1] <= p[3] && p[2] <= p[3]));
+}
+
+/// Glowing Edges sees transparency beyond every side of the raster: a solid square glows alike at
+/// its left and right edges (the right one doesn't read the next row's first pixel).
+#[test]
+fn glowing_edges_glow_alike_on_every_side() {
+    let (w, h) = (9, 9);
+    let mut out = image(w, h, |_, _| [180, 180, 180, 255]);
+    fx("stylize.glowingEdges", json!({"edgeWidth": 1, "smoothness": 1, "edgeBrightness": 20})).apply(&mut out, w, h, &space(w, h));
+    let (left, right, top, bottom) = (at(&out, w, 0, 4), at(&out, w, 8, 4), at(&out, w, 4, 0), at(&out, w, 4, 8));
+    assert!(left[0] > 0 && left == right && top == bottom, "{left:?} {right:?} {top:?} {bottom:?}");
+    assert!(at(&out, w, 4, 4)[0] < left[0], "the inside stays darker than the edges");
 }
 
 #[test]