diff --git a/crates/functions/src/math.rs b/crates/functions/src/math.rs
index 6d4cdcf58..f6a3b2efa 100644
--- a/crates/functions/src/math.rs
+++ b/crates/functions/src/math.rs
@@ -694,6 +694,16 @@ pub(crate) fn specs() -> Vec<FnSpec> {
         f!("ROUNDDOWN", 2, 2, MathTrig, S, "ROUNDDOWN(number, num_digits)", "Rounds a number toward zero to a given number of digits.", rounddown),
         f!("MROUND", 2, 2, MathTrig, S, "MROUND(number, multiple)", "Rounds a number to the nearest multiple.", mround),
         f!("CEILING", 2, 2, Compatibility, S, "CEILING(number, significance)", "Rounds a number up to a multiple of significance.", ceiling),
+        f!(
+            "ECMA.CEILING",
+            2,
+            2,
+            Compatibility,
+            S,
+            "ECMA.CEILING(number, significance)",
+            "Rounds a number up to a multiple of significance.",
+            ceiling
+        ),
         f!(
             "CEILING.MATH",
             1,
diff --git a/crates/functions/src/math/tests.rs b/crates/functions/src/math/tests.rs
index 14f72d1e1..503d4771c 100644
--- a/crates/functions/src/math/tests.rs
+++ b/crates/functions/src/math/tests.rs
@@ -101,6 +101,11 @@ fn rounding() {
     close(ev2("CEILING", 1.5, 0.1), 1.5);
     close(ev2("CEILING", 0.234, 0.01), 0.24);
     is_err(ev2("CEILING", 2.5, -1.0), Num);
+    // ECMA.CEILING is CEILING under a second name (Excel table from #2776).
+    close(ev2("ECMA.CEILING", 1.5, 1.0), 2.0);
+    close(ev2("ECMA.CEILING", -2.5, -2.0), -4.0);
+    close(ev2("ECMA.CEILING", 2.5, 0.0), 0.0);
+    is_err(ev2("ECMA.CEILING", 1.5, -1.0), Num);
     close(ev2("FLOOR", 3.7, 2.0), 2.0);
     close(ev2("FLOOR", -2.5, -2.0), -2.0);
     close(ev2("FLOOR", -2.5, 2.0), -4.0);
diff --git a/docs/function-parity.md b/docs/function-parity.md
index 12e239059..d9823e8bf 100644
--- a/docs/function-parity.md
+++ b/docs/function-parity.md
@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-26 · **Change:** minor (IMSQRT reproduces the stray real part Excel gives for negative reals, and the other IM* differences from Excel are listed; earlier: the LAMBDA row lists the recursion limit and its `#NUM!`, and the error a defined name holding an error gives when called; earlier: number text with accounting parentheses coerces like Excel 365; INDEX with one index on a 2-D reference is #REF! as in Excel; earlier: SUBTOTAL and AGGREGATE cap the cells they visit, #2175) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-15 · **Last updated:** 2026-10-27 · **Change:** minor (ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; earlier: IMSQRT reproduces the stray real part Excel gives for negative reals, and the other IM* differences from Excel are listed; earlier: the LAMBDA row lists the recursion limit and its `#NUM!`, and the error a defined name holding an error gives when called; earlier: number text with accounting parentheses coerces like Excel 365; INDEX with one index on a 2-D reference is #REF! as in Excel; earlier: SUBTOTAL and AGGREGATE cap the cells they visit, #2175) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Excel's worksheet functions, category by category, against GridCraft's function library. Part of
 [target-app-parity.md](target-app-parity.md); gaps feed [gaps.md](gaps.md).
@@ -20,8 +20,8 @@ Excel's worksheet functions, category by category, against GridCraft's function
   evaluator's special forms in `crates/calc/src/eval.rs` (`SPECIAL_FUNCTIONS`: IF, IFS, CHOOSE,
   OFFSET, INDIRECT, INDEX, SUBTOTAL, AGGREGATE, TEXT, LET, LAMBDA, MAP, REDUCE, SCAN, BYROW, BYCOL,
   MAKEARRAY…), excluding the test-only `ADD2`. Every one is an Excel name.
-- **Not on Microsoft's list:** USDOLLAR, a legacy function Excel still evaluates (like DOLLAR),
-  is in our library as a Compatibility function for files that use it. It is not counted above.
+- **Not on Microsoft's list:** USDOLLAR and ECMA.CEILING, legacy functions Excel still evaluates (like DOLLAR),
+  are in our library as Compatibility functions for files that use them. They are not counted above.
 - **Working** excludes stubs that return an error by design: the 7 CUBE functions (`#N/A`, no
   cube connections) and WEBSERVICE and FILTERXML (`#VALUE!`). Excel for Mac also lacks
   WEBSERVICE and FILTERXML; Excel for Windows has them.
@@ -124,6 +124,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-27 | minor | ECMA.CEILING added to the functions that are in our library but not on Microsoft's list (with USDOLLAR), so the counts don't change |
 | 2026-10-26 | minor | IMSQRT uses Excel's polar route with its cosine reduction, so `IMSQRT("-4")` is `1.22514845490862E-16+2i` as in Excel (exact `2i` before); the rows list the IM* differences still open |
 | 2026-10-25 | minor | LAMBDA row: a LAMBDA that calls itself more than 140 times, and a formula nested past the depth limit, give `#NUM!` (#1809; nesting gave `#CALC!` before). `=Foo(1)` where the defined name Foo holds `#N/A` gives `#N/A`, not `#NAME?` |
 | 2026-10-23 | minor | Number text coercion (VALUE, arithmetic, typed entry): a dollar sign before accounting parentheses (`$(1,234)`, `$ (5)`) and a percent sign after them (`(5)%`) read as negatives; `(-5)`, `((5))`, `($-5)`, `$5%`, `$(5)%` and dates or times in parentheses are `#VALUE!`, as observed in Excel 365 |