diff --git a/packages/tui/CHANGELOG.md b/packages/tui/CHANGELOG.md
index d12b9edd..a5bd3a2d 100644
--- a/packages/tui/CHANGELOG.md
+++ b/packages/tui/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixed
 
+- Fixed `ProcessTerminal` to fall back to `COLUMNS` and `LINES` before defaulting to 80x24 dimensions ([#4004](https://github.com/badlogic/pi-mono/issues/4004))
 - Fixed editor rendering artifacts for Thai Sara Am and Lao AM vowel characters ([#3904](https://github.com/badlogic/pi-mono/issues/3904))
 
 ## [0.70.6] - 2026-04-28
diff --git a/packages/tui/src/terminal.ts b/packages/tui/src/terminal.ts
index 0f657307..60eb0359 100644
--- a/packages/tui/src/terminal.ts
+++ b/packages/tui/src/terminal.ts
@@ -327,11 +327,11 @@ export class ProcessTerminal implements Terminal {
 	}
 
 	get columns(): number {
-		return process.stdout.columns || 80;
+		return process.stdout.columns || Number(process.env.COLUMNS) || 80;
 	}
 
 	get rows(): number {
-		return process.stdout.rows || 24;
+		return process.stdout.rows || Number(process.env.LINES) || 24;
 	}
 
 	moveBy(lines: number): void {
diff --git a/packages/tui/test/terminal.test.ts b/packages/tui/test/terminal.test.ts
new file mode 100644
index 00000000..7099b3df
--- /dev/null
+++ b/packages/tui/test/terminal.test.ts
@@ -0,0 +1,45 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import { ProcessTerminal } from "../src/terminal.js";
+
+describe("ProcessTerminal dimensions", () => {
+	it("falls back to COLUMNS and LINES before default dimensions", () => {
+		const previousColumnsDescriptor = Object.getOwnPropertyDescriptor(process.stdout, "columns");
+		const previousRowsDescriptor = Object.getOwnPropertyDescriptor(process.stdout, "rows");
+		const previousColumns = process.env.COLUMNS;
+		const previousLines = process.env.LINES;
+
+		try {
+			Object.defineProperty(process.stdout, "columns", { value: undefined, configurable: true });
+			Object.defineProperty(process.stdout, "rows", { value: undefined, configurable: true });
+			process.env.COLUMNS = "123";
+			process.env.LINES = "45";
+
+			const terminal = new ProcessTerminal();
+
+			assert.equal(terminal.columns, 123);
+			assert.equal(terminal.rows, 45);
+		} finally {
+			if (previousColumnsDescriptor) {
+				Object.defineProperty(process.stdout, "columns", previousColumnsDescriptor);
+			} else {
+				Reflect.deleteProperty(process.stdout, "columns");
+			}
+			if (previousRowsDescriptor) {
+				Object.defineProperty(process.stdout, "rows", previousRowsDescriptor);
+			} else {
+				Reflect.deleteProperty(process.stdout, "rows");
+			}
+			if (previousColumns === undefined) {
+				delete process.env.COLUMNS;
+			} else {
+				process.env.COLUMNS = previousColumns;
+			}
+			if (previousLines === undefined) {
+				delete process.env.LINES;
+			} else {
+				process.env.LINES = previousLines;
+			}
+		}
+	});
+});