diff --git a/dictionaries/CallMap.php b/dictionaries/CallMap.php
index 85f21fac2f2..47b8bb4b3c2 100644
--- a/dictionaries/CallMap.php
+++ b/dictionaries/CallMap.php
@@ -511,7 +511,8 @@
 'BadMethodCallException::getPrevious' => ['?Throwable'],
 'BadMethodCallException::getTrace' => ['list<array{file?:string,line?:int,function:string,class?:class-string,type?:\'::\'|\'->\',args?:array<mixed>}>'],
 'BadMethodCallException::getTraceAsString' => ['string'],
-'base64_decode' => ['string|false', 'string'=>'string', 'strict='=>'bool'],
+'base64_decode' => ['string', 'string'=>'string', 'strict='=>'false'],
+'base64_decode\'1' => ['string|false', 'string'=>'string', 'strict='=>'true'],
 'base64_encode' => ['string', 'string'=>'string'],
 'base_convert' => ['string', 'num'=>'string', 'from_base'=>'int', 'to_base'=>'int'],
 'basename' => ['string', 'path'=>'string', 'suffix='=>'string'],
diff --git a/dictionaries/CallMap_historical.php b/dictionaries/CallMap_historical.php
index 82344f93642..e0d17e99491 100644
--- a/dictionaries/CallMap_historical.php
+++ b/dictionaries/CallMap_historical.php
@@ -9404,7 +9404,8 @@
     'atan' => ['float', 'num'=>'float'],
     'atan2' => ['float', 'y'=>'float', 'x'=>'float'],
     'atanh' => ['float', 'num'=>'float'],
-    'base64_decode' => ['string|false', 'string'=>'string', 'strict='=>'bool'],
+    'base64_decode' => ['string', 'string'=>'string', 'strict='=>'false'],
+    'base64_decode\'1' => ['string|false', 'string'=>'string', 'strict='=>'true'],
     'base64_encode' => ['string', 'string'=>'string'],
     'base_convert' => ['string', 'num'=>'string', 'from_base'=>'int', 'to_base'=>'int'],
     'basename' => ['string', 'path'=>'string', 'suffix='=>'string'],
diff --git a/stubs/CoreGenericFunctions.phpstub b/stubs/CoreGenericFunctions.phpstub
index 5e2640e1a1f..f3fa3bbc1c3 100644
--- a/stubs/CoreGenericFunctions.phpstub
+++ b/stubs/CoreGenericFunctions.phpstub
@@ -1559,7 +1559,10 @@ function unpack(string $format, string $string, int $offset = 0) {}
 /**
  * @psalm-pure
  *
+ * @template T of bool
+ * @param T $strict
  * @return string|false
+ * @psalm-return (T is false ? string : string|false)
  *
  * @psalm-flow ($string) -> return
  * @psalm-ignore-falsable-return