diff --git a/src/ir_lower/expr/mod.rs b/src/ir_lower/expr/mod.rs
index 71a2f70ede..6a5dd559e3 100644
--- a/src/ir_lower/expr/mod.rs
+++ b/src/ir_lower/expr/mod.rs
@@ -7623,7 +7623,19 @@ fn release_stringified_source_if_owned(
         return;
     }
     match ctx.builder.value_php_type(source.value).codegen_repr() {
-        PhpType::Object(_) | PhpType::Array(_) | PhpType::AssocArray { .. } => {
+        // Boxed Mixed sources are safe to release here as well: the backend
+        // lowers `cast Mixed -> Str` through `__rt_mixed_cast_string`, which
+        // detaches the result from the box (string payloads are persisted into
+        // an independent copy; int/float/bool payloads render into fresh
+        // buffers), so the produced string never aliases the released cell.
+        // Skipping Mixed leaked every owned boxed temporary that flowed into a
+        // string coercion — e.g. `echo $row[1] . "\n"` inside a by-value
+        // `foreach` leaked the `$row[1]` element box each iteration (issue
+        // #527). `Union` codegen-reprs to `Mixed`, so this arm covers it too.
+        PhpType::Object(_)
+        | PhpType::Array(_)
+        | PhpType::AssocArray { .. }
+        | PhpType::Mixed => {
             crate::ir_lower::ownership::release_if_owned(ctx, source, span);
         }
         _ => {}
diff --git a/tests/codegen/runtime_gc/regressions.rs b/tests/codegen/runtime_gc/regressions.rs
index bdf32578f7..96bcde0af2 100644
--- a/tests/codegen/runtime_gc/regressions.rs
+++ b/tests/codegen/runtime_gc/regressions.rs
@@ -1230,3 +1230,74 @@ echo "done";
         "promoting an indexed array literal to hash storage must free the source array (issue #408)"
     );
 }
+
+/// Regression test for issue #527: a by-value `foreach` over an array of arrays
+/// whose body string-coerces an element read (`echo $row[1] . "\n"`) must not
+/// leak. The `$row[1]` read produces an owned boxed Mixed temporary; the
+/// implicit Mixed→string coercion detaches its result, so the source box must
+/// be released after the cast instead of leaking two heap blocks per iteration
+/// (the box plus the string payload it owns).
+#[test]
+fn test_regression_527_foreach_value_element_string_coercion_heap_debug_clean() {
+    let out = compile_and_run_with_heap_debug(
+        r#"<?php
+$a = [];
+for ($i = 0; $i < 4; $i++) { $a[] = ['kw', 'word' . $i]; }
+foreach ($a as $row) { echo $row[1] . "\n"; }
+"#,
+    );
+    assert!(out.success, "program failed: {}", out.stderr);
+    assert_eq!(out.stdout, "word0\nword1\nword2\nword3\n");
+    assert!(
+        out.stderr.contains("HEAP DEBUG: leak summary: clean"),
+        "expected a clean heap, got: {}",
+        out.stderr
+    );
+}
+
+/// Regression test for issue #527 (post-loop semantics): after a by-value
+/// `foreach` ends, the loop variable must still hold the LAST element like PHP,
+/// and string-coercing an element of that surviving copy must release the
+/// element box so the heap stays clean at exit.
+#[test]
+fn test_regression_527_foreach_value_var_survives_loop_and_heap_stays_clean() {
+    let out = compile_and_run_with_heap_debug(
+        r#"<?php
+$a = [];
+for ($i = 0; $i < 4; $i++) { $a[] = ['kw', 'word' . $i]; }
+foreach ($a as $row) {}
+echo $row[1] . "\n";
+"#,
+    );
+    assert!(out.success, "program failed: {}", out.stderr);
+    assert_eq!(out.stdout, "word3\n");
+    assert!(
+        out.stderr.contains("HEAP DEBUG: leak summary: clean"),
+        "expected a clean heap, got: {}",
+        out.stderr
+    );
+}
+
+/// Regression test for issue #527 (key + value form): iterating an associative
+/// array of arrays with string keys binds both an owned key copy and an owned
+/// value copy per iteration; string-coercing `$row[1]` inside the body must
+/// release the element box each iteration and end with a clean heap.
+#[test]
+fn test_regression_527_foreach_assoc_key_value_element_coercion_heap_debug_clean() {
+    let out = compile_and_run_with_heap_debug(
+        r#"<?php
+$m = [];
+$m['alpha'] = ['kw', 'wordA'];
+$m['beta'] = ['kw', 'wordB'];
+$m['gamma'] = ['kw', 'wordC'];
+foreach ($m as $k => $row) { echo $k . '=' . $row[1] . "\n"; }
+"#,
+    );
+    assert!(out.success, "program failed: {}", out.stderr);
+    assert_eq!(out.stdout, "alpha=wordA\nbeta=wordB\ngamma=wordC\n");
+    assert!(
+        out.stderr.contains("HEAP DEBUG: leak summary: clean"),
+        "expected a clean heap, got: {}",
+        out.stderr
+    );
+}