diff --git a/src/Type/Accessory/AccessoryDecimalIntegerStringType.php b/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
index d965eb0ebc..ebe0d3ce67 100644
--- a/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
+++ b/src/Type/Accessory/AccessoryDecimalIntegerStringType.php
@@ -205,14 +205,13 @@ public function unsetOffset(Type $offsetType): Type
 
 	public function toNumber(): Type
 	{
-		if ($this->inverse) {
-			return new UnionType([
-				$this->toInteger(),
-				$this->toFloat(),
-			]);
-		}
-
-		return $this->toInteger();
+		// Decimal integer strings larger than PHP_INT_MAX (or smaller than
+		// PHP_INT_MIN) overflow to float when coerced to a number, so the
+		// numeric coercion is int|float even for non-inverse values.
+		return new UnionType([
+			$this->toInteger(),
+			$this->toFloat(),
+		]);
 	}
 
 	public function toAbsoluteNumber(): Type
diff --git a/tests/PHPStan/Analyser/nsrt/bug-14786.php b/tests/PHPStan/Analyser/nsrt/bug-14786.php
new file mode 100644
index 0000000000..b82afeb402
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-14786.php
@@ -0,0 +1,38 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14786;
+
+use function PHPStan\Testing\assertType;
+
+/** @param decimal-int-string $s */
+function unaryPlus(string $s): void
+{
+	// big decimal-int-strings overflow PHP_INT_MAX and become float
+	assertType('float|int', +$s);
+}
+
+/** @param non-decimal-int-string $s */
+function unaryPlusNonDecimal(string $s): void
+{
+	assertType('float|int', +$s);
+}
+
+/** @param numeric-string $s */
+function unaryPlusNumeric(string $s): void
+{
+	assertType('float|int', +$s);
+}
+
+/** @param decimal-int-string $s */
+function intval(string $s): void
+{
+	// explicit int cast never overflows to float
+	assertType('int', (int) $s);
+}
+
+/** @param decimal-int-string $s */
+function arithmetic(string $s): void
+{
+	assertType('float|int', $s + 1);
+	assertType('float|int', $s * 2);
+}
diff --git a/tests/PHPStan/Analyser/nsrt/decimal-int-string.php b/tests/PHPStan/Analyser/nsrt/decimal-int-string.php
index fe5c5fdd52..e44175ac9b 100644
--- a/tests/PHPStan/Analyser/nsrt/decimal-int-string.php
+++ b/tests/PHPStan/Analyser/nsrt/decimal-int-string.php
@@ -18,7 +18,7 @@ public function doFoo(string $s): void
 
 		assertType('bool', (bool) $s);
 
-		assertType('int', $s + $s);
+		assertType('float|int', $s + $s);
 	}
 
 	/**
diff --git a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
index 8cf7ea1ba1..aa87e10e10 100644
--- a/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
+++ b/tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php
@@ -1367,4 +1367,10 @@ public function testBug6211(): void
 		]);
 	}
 
+	public function testBug14786(): void
+	{
+		$this->treatPhpDocTypesAsCertain = true;
+		$this->analyse([__DIR__ . '/data/bug-14786.php'], []);
+	}
+
 }
diff --git a/tests/PHPStan/Rules/Comparison/data/bug-14786.php b/tests/PHPStan/Rules/Comparison/data/bug-14786.php
new file mode 100644
index 0000000000..db5b4d12bb
--- /dev/null
+++ b/tests/PHPStan/Rules/Comparison/data/bug-14786.php
@@ -0,0 +1,17 @@
+<?php declare(strict_types = 1);
+
+namespace Bug14786;
+
+// example inspired by nikic/PHP-Parser ParserAbstract::parseNumber()
+/** @param decimal-int-string $str */
+function parseNumber(string $str): int|float
+{
+	// big decimal-int-strings overflow PHP_INT_MAX and become float,
+	// so is_int() is no longer always true.
+	$num = +$str;
+	if (!is_int($num)) {
+		return $num;
+	}
+
+	return $num;
+}