diff --git a/ext/standard/math.c b/ext/standard/math.c
index 6b16b0755f69b..2f6743865b464 100644
--- a/ext/standard/math.c
+++ b/ext/standard/math.c
@@ -177,6 +177,10 @@ PHPAPI double _php_math_round(double value, int places, int mode) {
 		return value;
 	}
 
+	if (places == 0) {
+		return php_round_helper(value, mode);
+	}
+
 	places = places < INT_MIN+1 ? INT_MIN+1 : places;
 	precision_places = 14 - php_intlog10abs(value);
 
diff --git a/ext/standard/tests/math/round_gh12143_5.phpt b/ext/standard/tests/math/round_gh12143_5.phpt
new file mode 100644
index 0000000000000..9f05628e5de84
--- /dev/null
+++ b/ext/standard/tests/math/round_gh12143_5.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-12143: Test rounding of 1.4999999999999998.
+--FILE--
+<?php
+foreach ([
+    1.4999999999999998,
+    -1.4999999999999998,
+] as $number) {
+    foreach ([
+        'PHP_ROUND_HALF_UP',
+        'PHP_ROUND_HALF_DOWN',
+        'PHP_ROUND_HALF_EVEN',
+        'PHP_ROUND_HALF_ODD',
+    ] as $mode) {
+        printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
+    }
+}
+?>
+--EXPECT--
+PHP_ROUND_HALF_UP   : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_DOWN : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_EVEN : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_ODD  : +1.4999999999999998 -> +1
+PHP_ROUND_HALF_UP   : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_DOWN : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_EVEN : -1.4999999999999998 -> -1
+PHP_ROUND_HALF_ODD  : -1.4999999999999998 -> -1
diff --git a/ext/standard/tests/math/round_gh12143_6.phpt b/ext/standard/tests/math/round_gh12143_6.phpt
new file mode 100644
index 0000000000000..07b1cc73ce615
--- /dev/null
+++ b/ext/standard/tests/math/round_gh12143_6.phpt
@@ -0,0 +1,27 @@
+--TEST--
+GH-12143: Test rounding of 4503599627370495.5.
+--FILE--
+<?php
+foreach ([
+    4503599627370495.5,
+    -4503599627370495.5,
+] as $number) {
+    foreach ([
+        'PHP_ROUND_HALF_UP',
+        'PHP_ROUND_HALF_DOWN',
+        'PHP_ROUND_HALF_EVEN',
+        'PHP_ROUND_HALF_ODD',
+    ] as $mode) {
+        printf("%-20s: %+.17g -> %+.17g\n", $mode, $number, round($number, 0, constant($mode)));
+    }
+}
+?>
+--EXPECT--
+PHP_ROUND_HALF_UP   : +4503599627370495.5 -> +4503599627370496
+PHP_ROUND_HALF_DOWN : +4503599627370495.5 -> +4503599627370495
+PHP_ROUND_HALF_EVEN : +4503599627370495.5 -> +4503599627370496
+PHP_ROUND_HALF_ODD  : +4503599627370495.5 -> +4503599627370495
+PHP_ROUND_HALF_UP   : -4503599627370495.5 -> -4503599627370496
+PHP_ROUND_HALF_DOWN : -4503599627370495.5 -> -4503599627370495
+PHP_ROUND_HALF_EVEN : -4503599627370495.5 -> -4503599627370496
+PHP_ROUND_HALF_ODD  : -4503599627370495.5 -> -4503599627370495