diff --git a/crates/functions/src/stat/distributions.rs b/crates/functions/src/stat/distributions.rs
index b1729b1fd..a3964ad80 100644
--- a/crates/functions/src/stat/distributions.rs
+++ b/crates/functions/src/stat/distributions.rs
@@ -571,7 +571,7 @@ pub(super) fn beta_dist(a: &[Arg], _: C) -> R<Value> {
     if cum {
         return num_val(reg_inc_beta(z, al, be));
     }
-    if (z == 0.0 && al < 1.0) || (z == 1.0 && be < 1.0) {
+    if (z == 0.0 && al <= 1.0) || (z == 1.0 && be <= 1.0) {
         return Err(CellError::Num);
     }
     let lp = if z == 0.0 || z == 1.0 {
diff --git a/crates/functions/src/stat/tests.rs b/crates/functions/src/stat/tests.rs
index c783cc492..74bd6b75e 100644
--- a/crates/functions/src/stat/tests.rs
+++ b/crates/functions/src/stat/tests.rs
@@ -518,6 +518,19 @@ fn continuous() {
     is_err(ev("GAMMA", vec![n(0.0)]), CellError::Num);
     close_tol(ev("BETA.DIST", vec![n(2.0), n(8.0), n(10.0), b(true), n(1.0), n(3.0)]), 0.6854706, D7);
     close_tol(ev("BETA.DIST", vec![n(2.0), n(8.0), n(10.0), b(false), n(1.0), n(3.0)]), 1.4837646, D7);
+    is_err(ev("BETA.DIST", vec![n(0.0), n(1.0), n(1.0), b(false)]), CellError::Num);
+    is_err(ev("BETA.DIST", vec![n(1.0), n(1.0), n(1.0), b(false)]), CellError::Num);
+    is_err(ev("BETA.DIST", vec![n(0.0), n(0.5), n(2.0), b(false)]), CellError::Num);
+    is_err(ev("BETA.DIST", vec![n(1.0), n(2.0), n(0.5), b(false)]), CellError::Num);
+    close(ev("BETA.DIST", vec![n(0.0), n(2.0), n(1.0), b(false)]), 0.0);
+    close(ev("BETA.DIST", vec![n(1.0), n(1.0), n(2.0), b(false)]), 0.0);
+    close(ev("BETA.DIST", vec![n(0.0), n(1.0), n(1.0), b(true)]), 0.0);
+    close(ev("BETA.DIST", vec![n(1.0), n(1.0), n(1.0), b(true)]), 1.0);
+    is_err(ev("BETA.DIST", vec![n(2.0), n(1.0), n(2.0), b(false), n(2.0), n(6.0)]), CellError::Num);
+    is_err(ev("BETA.DIST", vec![n(6.0), n(2.0), n(1.0), b(false), n(2.0), n(6.0)]), CellError::Num);
+    close(ev("BETA.DIST", vec![n(4.0), n(1.0), n(1.0), b(false), n(2.0), n(6.0)]), 0.25);
+    close(ev("BETA.DIST", vec![n(2.0), n(1.0), n(1.0), b(true), n(2.0), n(6.0)]), 0.0);
+    close(ev("BETA.DIST", vec![n(6.0), n(1.0), n(1.0), b(true), n(2.0), n(6.0)]), 1.0);
     close_tol(ev("BETADIST", vec![n(2.0), n(8.0), n(10.0), n(1.0), n(3.0)]), 0.6854706, D7);
     close_tol(ev("BETA.INV", vec![n(0.685470581), n(8.0), n(10.0), n(1.0), n(3.0)]), 2.0, D7);
     close_tol(ev("BETAINV", vec![n(0.685470581), n(8.0), n(10.0), n(1.0), n(3.0)]), 2.0, D7);
diff --git a/docs/function-parity.md b/docs/function-parity.md
index 9d8035715..f9d673cbf 100644
--- a/docs/function-parity.md
+++ b/docs/function-parity.md
@@ -1,6 +1,6 @@
 # Function parity: worksheet functions and formulas
 
-> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (BINOM.DIST and BINOM.DIST.RANGE refuse trial counts above 2,147,483,646 after truncation; earlier: WEIBULL.DIST density is zero at x=0, including shape below one, as in Excel; earlier: 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) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (BETA.DIST density returns `#NUM!` when an endpoint's corresponding shape parameter is less than or equal to 1; earlier: BINOM.DIST and BINOM.DIST.RANGE refuse trial counts above 2,147,483,646 after truncation) · **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).
@@ -102,6 +102,7 @@ This improves series preparation; it does not change the model-fitting or season
 |---|---|
 | BINOM.DIST / BINOM.DIST.RANGE | Trial count is truncated, then must be at most 2,147,483,646; larger trials return `#NUM!`. |
 
+| BETA.DIST | Density mode returns `#NUM!` at the lower or upper interval endpoint when the corresponding shape parameter is less than or equal to 1; cumulative endpoint results remain 0 and 1. |
 **~82% ready.** The library is broad and has 96 test functions in `crates/functions` with many
 assertions each, but there is no conformance suite against Excel-computed results, and user
 reports keep finding edge cases: MIN() with no arguments (#138), COUNTBLANK past the used range
@@ -143,6 +144,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 | 2026-10-31 | minor | GAMMA.DIST density at x=0 and shape 1 returns `#NUM!` for all positive scales; the cumulative branch and other shape boundaries are unchanged |
 | 2026-10-31 | minor | WEIBULL.DIST returns zero at x=0 in both density and cumulative modes, including shape below one; negative x remains `#NUM!` |
 | 2026-10-31 | minor | BINOM.DIST and BINOM.DIST.RANGE reject trial counts above 2,147,483,646 after truncation |
+| 2026-10-31 | minor | BETA.DIST density returns `#NUM!` at the lower endpoint with alpha less than or equal to 1 and upper endpoint with beta less than or equal to 1; cumulative behavior is unchanged |
 | 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?` |