diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2565a768..86be590b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 
 ### Fixed
 
+- Fixed issue with _ spacing character in number format mask corrumpting output from toFormattedString() [Issue 1924#](https://github.com/PHPOffice/PhpSpreadsheet/issues/1924) [PR #1927](https://github.com/PHPOffice/PhpSpreadsheet/pull/1927)
 - Fix for [Issue #1887](https://github.com/PHPOffice/PhpSpreadsheet/issues/1887) - Lose Track of Selected Cells After Save
 - Fixed issue with Xlsx@listWorksheetInfo not returning any data
 - Fixed invalid arguments triggering mb_substr() error in LEFT(), MID() and RIGHT() text functions. [Issue #640](https://github.com/PHPOffice/PhpSpreadsheet/issues/640)
diff --git a/src/PhpSpreadsheet/Style/NumberFormat.php b/src/PhpSpreadsheet/Style/NumberFormat.php
index a623657b..3c6985a2 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat.php
@@ -848,7 +848,7 @@ class NumberFormat extends Supervisor
         );
 
         // Convert any other escaped characters to quoted strings, e.g. (\T to "T")
-        $format = preg_replace('/(\\\(((.)(?!((AM\/PM)|(A\/P))))|([^ ])))(?=(?:[^"]|"[^"]*")*$)/u', '"${2}"', $format);
+        $format = preg_replace('/(\\\(((.)(?!((AM\/PM)|(A\/P))))|([^ ])))(?=(?:[^"]|"[^"]*")*$)/ui', '"${2}"', $format);
 
         // Get the sections, there can be up to four sections, separated with a semi-colon (but only if not a quoted literal)
         $sections = preg_split('/(;)(?=(?:[^"]|"[^"]*")*$)/u', $format);
@@ -857,7 +857,7 @@ class NumberFormat extends Supervisor
 
         // In Excel formats, "_" is used to add spacing,
         //    The following character indicates the size of the spacing, which we can't do in HTML, so we just use a standard space
-        $format = preg_replace('/_./', ' ', $format);
+        $format = preg_replace('/_(.)/ui', ' ${1}', $format);
 
         // Let's begin inspecting the format and converting the value to a formatted string
 
diff --git a/tests/data/Style/NumberFormat.php b/tests/data/Style/NumberFormat.php
index 81bb90ae..db14b0e1 100644
--- a/tests/data/Style/NumberFormat.php
+++ b/tests/data/Style/NumberFormat.php
@@ -128,6 +128,11 @@ return [
         12345.678900000001,
         '#,##0.000\ [$]',
     ],
+    'Spacing Character' => [
+        '826.00  €',
+        826,
+        '#,##0.00 _€',
+    ],
     [
         '5.68',
         5.6788999999999996,
@@ -294,12 +299,12 @@ return [
         '[$-1010409]#,##0.00;-#,##0.00',
     ],
     [
-        ' $ 23.06 ',
+        ' ($ 23.06 )',
         23.0597,
         '_("$"* #,##0.00_);_("$"* \(#,##0.00\);_("$"* "-"??_);_(@_)',
     ],
     [
-        ' € 13.03 ',
+        ' (€ 13.03 )',
         13.0316,
         '_("€"* #,##0.00_);_("€"* \(#,##0.00\);_("€"* "-"??_);_(@_)',
     ],