diff --git a/lib/VM/BackedEnum.php b/lib/VM/BackedEnum.php
index 8a2693935ef..50a1ce734fa 100644
--- a/lib/VM/BackedEnum.php
+++ b/lib/VM/BackedEnum.php
@@ -30,6 +30,16 @@ public static function caseForValue(ClassEntry $enum, Variable $value): ?EnumCas
         }
         EnumSupport::ensureBackedEnumValuesUnique($enum);
         $normalized = self::normalizeBackingArgument($enum, $value->resolveIndirect());
+        $match = self::matchCaseForBackingValue($enum, $normalized);
+        if (null !== $match) {
+            return $match;
+        }
+
+        return self::matchCaseForBackingValueFromConstants($enum, $normalized);
+    }
+
+    private static function matchCaseForBackingValue(ClassEntry $enum, Variable $normalized): ?EnumCaseEntry
+    {
         foreach ($enum->enumCases as $case) {
             $backing = self::caseBackingScalar($enum->backedType, $case['value']);
             if (!self::backingValuesMatch($enum->backedType, $backing, $normalized)) {
@@ -42,6 +52,31 @@ public static function caseForValue(ClassEntry $enum, Variable $value): ?EnumCas
         return null;
     }
 
+    /**
+     * Fallback when {@see ClassEntry::$enumCases} is empty or stale but case constants remain (#9603).
+     *
+     * @see Zend/zend_enum.c — zend_enum_from_case() backed-value hash
+     */
+    private static function matchCaseForBackingValueFromConstants(
+        ClassEntry $enum,
+        Variable $normalized
+    ): ?EnumCaseEntry {
+        foreach ($enum->constants as $memberLc => $stored) {
+            $caseName = EnumSupport::enumCaseNameForConstantMember($enum, $memberLc);
+            if (null === $caseName) {
+                continue;
+            }
+            $backing = self::caseBackingScalar($enum->backedType, $stored);
+            if (!self::backingValuesMatch($enum->backedType, $backing, $normalized)) {
+                continue;
+            }
+
+            return new EnumCaseEntry($enum, $caseName, clone $backing);
+        }
+
+        return null;
+    }
+
     /**
      * Canonical enum case variable for a matched case name (Zend singleton identity, #5533).
      */
diff --git a/lib/VM/EnumFromHandler.php b/lib/VM/EnumFromHandler.php
index 91ddf399b31..8f1fb26e4c4 100644
--- a/lib/VM/EnumFromHandler.php
+++ b/lib/VM/EnumFromHandler.php
@@ -24,17 +24,18 @@ public function __construct(
 
     public function execute(Frame $frame): void
     {
-        EnumSupport::ensureBackedEnumValuesUnique($this->enum);
+        $enum = EnumSupport::resolveRuntimeEnumClass($frame->vmContext, $this->enum);
+        EnumSupport::ensureBackedEnumValuesUnique($enum);
         if (\count($frame->calledArgs) < 1) {
             throw new \LogicException(
                 $this->getName().'() requires exactly 1 argument in this compiler build'
             );
         }
         $arg = $frame->calledArgs[0];
-        $match = BackedEnum::caseForValue($this->enum, $arg);
+        $match = BackedEnum::caseForValue($enum, $arg);
         if (null === $match) {
             if (!$this->try) {
-                throw new \ValueError(BackedEnum::valueErrorMessage($this->enum, $arg));
+                throw new \ValueError(BackedEnum::valueErrorMessage($enum, $arg));
             }
             if (null !== $frame->returnVar) {
                 $frame->returnVar->null();
@@ -43,7 +44,7 @@ public function execute(Frame $frame): void
             return;
         }
         if (null !== $frame->returnVar) {
-            $canonical = BackedEnum::canonicalCaseVariable($this->enum, $match->caseName);
+            $canonical = BackedEnum::canonicalCaseVariable($enum, $match->caseName);
             if (null !== $canonical && EnumCaseSupport::isEnumCaseVariable($canonical)) {
                 $frame->returnVar->copyFrom($canonical);
             } else {
diff --git a/test/repro/issue_9603_enum_from.php b/test/repro/issue_9603_enum_from.php
new file mode 100644
index 00000000000..645583d350c
--- /dev/null
+++ b/test/repro/issue_9603_enum_from.php
@@ -0,0 +1,14 @@
+<?php
+enum E: string {
+    case A = 'a';
+}
+
+var_dump(E::tryFrom('b')); // Zend: NULL
+var_dump(E::tryFrom('a')); // Zend: enum(E::A)
+
+try {
+    E::from('a');
+    echo "from ok\n";
+} catch (ValueError $e) {
+    echo 'from fail: ', $e->getMessage(), "\n";
+}
diff --git a/test/unit/VmEnumCanonicalCaseVariableTest.php b/test/unit/VmEnumCanonicalCaseVariableTest.php
index 577cddb9bf9..27e39047e95 100644
--- a/test/unit/VmEnumCanonicalCaseVariableTest.php
+++ b/test/unit/VmEnumCanonicalCaseVariableTest.php
@@ -40,4 +40,27 @@ enum E: string { case A = 'x'; case B = 'y'; }
         $this->assertNotNull($canonical);
         $this->assertTrue(EnumCaseSupport::isEnumCaseVariable($canonical));
     }
+
+    /** Issue #9603 — from()/tryFrom() must resolve via constants when enumCases table is empty. */
+    public function testFromResolvesWhenEnumCasesTableEmpty(): void
+    {
+        $runtime = new Runtime();
+        $runtime->run($runtime->parseAndCompile(<<<'PHP'
+<?php
+enum E: string { case A = 'x'; case B = 'y'; }
+PHP, 'enum_decl.php'));
+        $enum = $runtime->vmContext->classes['e'];
+        $this->assertNotEmpty($enum->enumCases);
+        $enum->enumCases = [];
+
+        ob_start();
+        $runtime->run($runtime->parseAndCompile(<<<'PHP'
+<?php
+echo E::tryFrom('x')->name;
+echo E::from('y')->name;
+PHP, 'enum_from_empty_cases.php'));
+        $output = ob_get_clean();
+
+        $this->assertSame('AB', $output);
+    }
 }
diff --git a/test/unit/VmEnumFromTest.php b/test/unit/VmEnumFromTest.php
index 109a1513a02..b635a8fa639 100644
--- a/test/unit/VmEnumFromTest.php
+++ b/test/unit/VmEnumFromTest.php
@@ -141,4 +141,33 @@ enum Level: int { case Low = 1; }
         $this->expectExceptionMessage('Level::from(): Argument #1 ($value) must be of type int, string given');
         $runtime->run($block);
     }
+
+    /** Issue #9603 — exact maintainer repro: valid backing values resolve to enum cases. */
+    public function testIssue9603EnumFromTryFromRepro(): void
+    {
+        $code = <<<'PHP'
+<?php
+enum E: string {
+    case A = 'a';
+}
+
+var_export(E::tryFrom('b') === null);
+echo "\n";
+var_export(E::tryFrom('a')->name);
+echo "\n";
+try {
+    E::from('a');
+    echo "from ok\n";
+} catch (ValueError $e) {
+    echo 'from fail: ', $e->getMessage(), "\n";
+}
+PHP;
+        $runtime = new Runtime();
+        $block = $runtime->parseAndCompile($code, 'issue_9603_enum_from.php');
+        ob_start();
+        $runtime->run($block);
+        $output = ob_get_clean();
+
+        $this->assertSame("true\n'A'\nfrom ok\n", $output);
+    }
 }