diff --git a/src/Parser/ArrayOffsetNormalizingVisitor.php b/src/Parser/ArrayOffsetNormalizingVisitor.php
new file mode 100644
index 00000000000..40c525a142f
--- /dev/null
+++ b/src/Parser/ArrayOffsetNormalizingVisitor.php
@@ -0,0 +1,61 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Parser;
+
+use Override;
+use PhpParser\Node;
+use PhpParser\Node\Expr\ArrayDimFetch;
+use PhpParser\Node\Scalar\Int_;
+use PhpParser\Node\Scalar\InterpolatedString;
+use PhpParser\Node\Scalar\String_;
+use PhpParser\NodeVisitorAbstract;
+use PHPStan\DependencyInjection\AutowiredService;
+use function preg_match;
+
+/**
+ * `$a['k']` and `$a["k"]` read the same offset, but MutatingScope tracks types
+ * under the pretty-printed form of an expression, and the pretty printer
+ * reproduces the *source spelling* of a literal - so narrowing established
+ * through one spelling used to be invisible at the other, and reformatting a
+ * file changed the analysis result.
+ *
+ * Rewriting the offset literal to a canonical spelling here rather than in the
+ * printer keeps the printed form faithful everywhere else, so the expression
+ * text quoted back in error messages is unaffected outside of array offsets.
+ *
+ * Only the spelling attributes are touched, never a subnode, so rules see the
+ * same AST and format-preserving printing still reproduces the original source
+ * for these nodes.
+ */
+#[AutowiredService]
+final class ArrayOffsetNormalizingVisitor extends NodeVisitorAbstract
+{
+
+	#[Override]
+	public function enterNode(Node $node): ?Node
+	{
+		if (!$node instanceof ArrayDimFetch || $node->dim === null) {
+			return null;
+		}
+
+		$dim = $node->dim;
+		if ($dim instanceof String_) {
+			// Single quotes normally, double quotes when the value holds control
+			// characters - the same canonical form as ConstantStringType::export(),
+			// and the one that keeps the expression key free of newlines.
+			$dim->setAttribute(
+				'kind',
+				preg_match('/[\x00-\x1f]/', $dim->value) === 1
+					? String_::KIND_DOUBLE_QUOTED
+					: String_::KIND_SINGLE_QUOTED,
+			);
+		} elseif ($dim instanceof InterpolatedString) {
+			$dim->setAttribute('kind', String_::KIND_DOUBLE_QUOTED);
+		} elseif ($dim instanceof Int_) {
+			$dim->setAttribute('kind', Int_::KIND_DEC);
+		}
+
+		return null;
+	}
+
+}
diff --git a/tests/PHPStan/Analyser/nsrt/bug-15060.php b/tests/PHPStan/Analyser/nsrt/bug-15060.php
new file mode 100644
index 00000000000..eac694598f7
--- /dev/null
+++ b/tests/PHPStan/Analyser/nsrt/bug-15060.php
@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace Bug15060;
+
+use function PHPStan\Testing\assertType;
+
+function search($searchParams): void
+{
+	if (isset($searchParams['test'])) {
+		assertType('mixed~null', $searchParams['test']);
+		if ($searchParams["test"]) {
+			assertType("mixed~(0|0.0|''|'0'|array{}|false|null)", $searchParams['test']);
+			assertType("mixed~(0|0.0|''|'0'|array{}|false|null)", $searchParams["test"]);
+		}
+
+		if (is_array($searchParams["test"])) {
+			assertType('array<mixed, mixed>', $searchParams['test']);
+			assertType('array<mixed, mixed>', $searchParams["test"]);
+		}
+
+		if (is_array($searchParams["test"]) && $searchParams["test"]) {
+			assertType('non-empty-array<mixed, mixed>', $searchParams['test']);
+			assertType('non-empty-array<mixed, mixed>', $searchParams["test"]);
+		}
+	}
+}
+
+function otherStringSpellings($m): void
+{
+	if (is_array($m['test']) && $m['test']) {
+		assertType('non-empty-array<mixed, mixed>', $m['test']);
+		assertType('non-empty-array<mixed, mixed>', $m["test"]);
+		assertType('non-empty-array<mixed, mixed>', $m["\x74est"]);
+		assertType('non-empty-array<mixed, mixed>', $m[<<<'NOWDOC'
+			test
+			NOWDOC]);
+		assertType('non-empty-array<mixed, mixed>', $m[<<<HEREDOC
+			test
+			HEREDOC]);
+	}
+}
+
+function intSpellings($m): void
+{
+	if (is_array($m[1]) && $m[1]) {
+		assertType('non-empty-array<mixed, mixed>', $m[1]);
+		assertType('non-empty-array<mixed, mixed>', $m[0x1]);
+		assertType('non-empty-array<mixed, mixed>', $m[01]);
+		assertType('non-empty-array<mixed, mixed>', $m[0b1]);
+		assertType('mixed', $m[10]);
+	}
+}
+
+function interpolatedSpellings($m, string $k): void
+{
+	if (is_array($m["x$k"]) && $m["x$k"]) {
+		assertType('non-empty-array<mixed, mixed>', $m["x$k"]);
+		assertType('non-empty-array<mixed, mixed>', $m["x{$k}"]);
+		assertType('non-empty-array<mixed, mixed>', $m[<<<HEREDOC
+			x$k
+			HEREDOC]);
+	}
+}