diff --git a/src/display/canvas.js b/src/display/canvas.js
index 442b12e9cb0c2..9ad7b7e43a18d 100644
--- a/src/display/canvas.js
+++ b/src/display/canvas.js
@@ -3342,13 +3342,15 @@ class CanvasGraphics {
     // #compositeKnockoutSurface so it doesn't become part of the group
     // source itself.
     const backdropCtx = group.knockout && !group.isolated ? currentCtx : null;
-    // Non-isolated non-KO subgroup inside a KO parent: at endGroup we'll
-    // blend its elements against the outer KO running canvas (also frozen),
-    // so just record the flag here and read ctx.canvas at composite time.
+    // Non-isolated non-KO subgroup inside a KO parent, with inner compositing
+    // of its own: at endGroup we'll blend its elements against the outer KO
+    // running canvas (also frozen), so just record the flag here and read
+    // ctx.canvas at composite time.
     const hasInnerBackdrop =
       !group.isolated &&
       !group.knockout &&
       !group.smask &&
+      group.needsIsolation &&
       this.#knockoutGroupLevel > 0;
 
     // Pool the per-element shape mask for the lifetime of this KO group.
diff --git a/test/pdfs/.gitignore b/test/pdfs/.gitignore
index f114eb7b9424e..a0c521f326746 100644
--- a/test/pdfs/.gitignore
+++ b/test/pdfs/.gitignore
@@ -920,3 +920,4 @@
 !smask_luminosity_oob_transfer.pdf
 !operator_list_cycle.pdf
 !knockout_groups_test.pdf
+!issue18032.pdf
diff --git a/test/pdfs/issue18032.pdf b/test/pdfs/issue18032.pdf
new file mode 100644
index 0000000000000..9457d54ebe0b8
Binary files /dev/null and b/test/pdfs/issue18032.pdf differ
diff --git a/test/test_manifest.json b/test/test_manifest.json
index ae2828583e001..adc5211c63109 100644
--- a/test/test_manifest.json
+++ b/test/test_manifest.json
@@ -14252,5 +14252,13 @@
     "rounds": 1,
     "type": "eq",
     "about": "Knockout groups composite-modes survey."
+  },
+  {
+    "id": "issue18032",
+    "file": "pdfs/issue18032.pdf",
+    "md5": "656234fde97953c4e3fc7698831590a9",
+    "rounds": 1,
+    "type": "eq",
+    "about": "Non-isolated knockout group with a nested non-isolated subgroup over existing text."
   }
 ]