diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfb53eac..2e875d33 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,9 @@
 - Updates to data for USA and WGS84
 - Support for Irish polynomial transformation in the ETRS89 to TM75 direction (TM75 to ETRS89 was already supported)
 
+### Fixed
+- British and Irish Grid references were rounding rather than truncating causing a sometimes off-by-1 error
+
 ## [5.9.0] - 2024-08-04
 ### Changed
 - Updates to data for Czechia, Denmark, ETRS89, Germany, Martinique, Portugal, St Helena, UK and WGS84
diff --git a/src/Point/BritishNationalGridPoint.php b/src/Point/BritishNationalGridPoint.php
index bcb3552f..0af77b35 100644
--- a/src/Point/BritishNationalGridPoint.php
+++ b/src/Point/BritishNationalGridPoint.php
@@ -21,7 +21,6 @@
 use function strlen;
 use function strpos;
 use function substr;
-use function round;
 
 use const STR_PAD_LEFT;
 
@@ -97,8 +96,8 @@ protected function gridReference(int $length): array
 
         $x = $this->easting->asMetres()->getValue();
         $y = $this->northing->asMetres()->getValue();
-        $easting = str_pad((string) round($x), $halfLength, '0', STR_PAD_LEFT);
-        $northing = str_pad((string) round($y), $halfLength, '0', STR_PAD_LEFT);
+        $easting = str_pad((string) (int) $x, $halfLength, '0', STR_PAD_LEFT);
+        $northing = str_pad((string) (int) $y, $halfLength, '0', STR_PAD_LEFT);
 
         $adjustedX = $x + 1000000;
         $adjustedY = $y + 500000;
diff --git a/src/Point/IrishGridPoint.php b/src/Point/IrishGridPoint.php
index d9208cec..fc70d8d8 100644
--- a/src/Point/IrishGridPoint.php
+++ b/src/Point/IrishGridPoint.php
@@ -21,7 +21,6 @@
 use function strlen;
 use function strpos;
 use function substr;
-use function round;
 
 use const STR_PAD_LEFT;
 
@@ -96,8 +95,8 @@ protected function gridReference(int $length): array
 
         $x = $this->easting->asMetres()->getValue();
         $y = $this->northing->asMetres()->getValue();
-        $easting = str_pad((string) round($x), $halfLength, '0', STR_PAD_LEFT);
-        $northing = str_pad((string) round($y), $halfLength, '0', STR_PAD_LEFT);
+        $easting = str_pad((string) (int) $x, $halfLength, '0', STR_PAD_LEFT);
+        $northing = str_pad((string) (int) $y, $halfLength, '0', STR_PAD_LEFT);
 
         // second (minor) letter is 100km grid sq, origin at 0,0 of this square
         $minorSquaresEast = (int) $easting[0] % 5;