diff --git a/crates/functions/src/engineering.rs b/crates/functions/src/engineering.rs
index dbe6734d3..0baf2b2ca 100644
--- a/crates/functions/src/engineering.rs
+++ b/crates/functions/src/engineering.rs
@@ -25,7 +25,7 @@ fn base_source(a: &[Arg]) -> R<String> {
             Ok(number_to_text(n))
         }
         Value::Empty => Ok(String::new()),
-        v => Ok(v.to_text()?.trim().to_string()),
+        v => Ok(v.to_text()?.to_string()),
     }
 }
 
@@ -426,6 +426,21 @@ mod tests {
         is_text(ev("OCT2HEX", vec![n(100.0), n(4.0)]), "0040");
         is_text(ev("OCT2HEX", vec![n(7777777533.0)]), "FFFFFFFF5B");
         is_err(ev("BIN2DEC", vec![n(102.0)]), CellError::Num);
+        for (f, input) in [
+            ("BIN2DEC", " 10"),
+            ("BIN2DEC", "10 "),
+            ("BIN2DEC", "\t10"),
+            ("BIN2HEX", " 10"),
+            ("BIN2OCT", "10 "),
+            ("HEX2DEC", " 10"),
+            ("HEX2BIN", "10 "),
+            ("HEX2OCT", "\t10"),
+            ("OCT2DEC", " 10"),
+            ("OCT2BIN", "10 "),
+            ("OCT2HEX", "\t10"),
+        ] {
+            is_err(ev(f, vec![t(input)]), CellError::Num);
+        }
         is_err(ev("HEX2DEC", vec![t("GG")]), CellError::Num);
         is_err(ev("BIN2DEC", vec![t("11111111111")]), CellError::Num);
         is_err(ev("DEC2BIN", vec![t("abc")]), CellError::Value);
diff --git a/docs/function-parity.md b/docs/function-parity.md
index d9823e8bf..8fbfe52a5 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:** 2026-10-27 · **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
+> **Last reviewed:** 2026-10-31 · **Last updated:** 2026-10-31 · **Change:** minor (base conversion rejects surrounding whitespace in source strings, as observed in Excel; earlier: ECMA.CEILING listed with USDOLLAR as not on Microsoft's list; IMSQRT reproduces Excel's stray real part for negative reals) · **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).
@@ -124,6 +124,7 @@ workbooks; results checked in as data, not Excel files) and fixing what it finds
 
 | Date | Change | Summary |
 |---|---|---|
+| 2026-10-31 | minor | BIN2*, HEX2* and OCT2* reject surrounding spaces and tabs in source strings with `#NUM!`, matching Excel; plain unpadded values remain valid |
 | 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?` |