diff --git a/NEWS b/NEWS
index a4dd4063542bb..2f6d4ef952139 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,10 @@ PHP                                                                        NEWS
   . Fixed bug #77589 (Core dump using parse_ini_string with numeric sections).
     (Laruence)
 
+- COM:
+  . Fixed bug #77621 (Already defined constants are not properly reported).
+    (cmb)
+
 - PDO_OCI:
   . Support Oracle Database tracing attributes ACTION, MODULE,
     CLIENT_INFO, and CLIENT_IDENTIFIER. (Cameron Porter)
diff --git a/ext/com_dotnet/com_typeinfo.c b/ext/com_dotnet/com_typeinfo.c
index a0fa3c0749113..40f21aea6bda8 100644
--- a/ext/com_dotnet/com_typeinfo.c
+++ b/ext/com_dotnet/com_typeinfo.c
@@ -197,9 +197,10 @@ PHP_COM_DOTNET_API int php_com_import_typelib(ITypeLib *TL, int mode, int codepa
 				SysFreeString(bstr_ids);
 
 				/* sanity check for the case where the constant is already defined */
+				php_com_zval_from_variant(&value, pVarDesc->lpvarValue, codepage);
 				if ((exists = zend_get_constant(c.name)) != NULL) {
-					if (COMG(autoreg_verbose) && !compare_function(&results, &c.value, exists)) {
-						php_error_docref(NULL, E_WARNING, "Type library constant %s is already defined", c.name);
+					if (COMG(autoreg_verbose) && !compare_function(&results, &value, exists)) {
+						php_error_docref(NULL, E_WARNING, "Type library constant %s is already defined", ZSTR_VAL(c.name));
 					}
 					zend_string_release(c.name);
 					ITypeInfo_ReleaseVarDesc(TypeInfo, pVarDesc);
@@ -207,7 +208,6 @@ PHP_COM_DOTNET_API int php_com_import_typelib(ITypeLib *TL, int mode, int codepa
 				}
 
 				/* register the constant */
-				php_com_zval_from_variant(&value, pVarDesc->lpvarValue, codepage);
 				if (Z_TYPE(value) == IS_LONG) {
 					c.flags = mode;
 					ZVAL_LONG(&c.value, Z_LVAL(value));
diff --git a/ext/com_dotnet/tests/bug77621.phpt b/ext/com_dotnet/tests/bug77621.phpt
new file mode 100644
index 0000000000000..5c24494637f6a
--- /dev/null
+++ b/ext/com_dotnet/tests/bug77621.phpt
@@ -0,0 +1,18 @@
+--TEST--
+Bug #77621 (Already defined constants are not properly reported)
+--SKIPIF--
+<?php
+if (!extension_loaded('com_dotnet')) die('skip com_dotnet extension not available');
+?>
+--INI--
+com.autoregister_verbose=1
+--FILE--
+<?php
+define('ADSTYPE_INVALID', 0);
+$root = dirname(array_change_key_case($_SERVER, CASE_UPPER)['COMSPEC']);
+com_load_typelib("$root\activeds.tlb");
+?>
+===DONE===
+--EXPECTF--
+Warning: com_load_typelib(): Type library constant ADSTYPE_INVALID is already defined in %s on line %d
+===DONE===