diff --git a/src/Psalm/Checker/FunctionChecker.php b/src/Psalm/Checker/FunctionChecker.php
index 76656ee1a..18bffee40 100644
--- a/src/Psalm/Checker/FunctionChecker.php
+++ b/src/Psalm/Checker/FunctionChecker.php
@@ -135,6 +135,22 @@ class FunctionChecker extends FunctionLikeChecker
 
                     return $call_map_key === 'var_export' ? Type::getVoid() : Type::getBool();
 
+                case 'print_r':
+                    if (isset($call_args[1]->value->inferredType)) {
+                        $subject_type = $call_args[1]->value->inferredType;
+
+                        if ((string) $subject_type === 'true') {
+                            return Type::getString();
+                        }
+
+                        return new Type\Union([
+                            new Type\Atomic\TString,
+                            new Type\Atomic\TTrue
+                        ]);
+                    }
+
+                    return Type::getTrue();
+
                 case 'getenv':
                     return new Type\Union([new Type\Atomic\TString, new Type\Atomic\TFalse]);
 
diff --git a/tests/FunctionCallTest.php b/tests/FunctionCallTest.php
index 2a933c757..ed360bf16 100644
--- a/tests/FunctionCallTest.php
+++ b/tests/FunctionCallTest.php
@@ -960,6 +960,14 @@ class FunctionCallTest extends TestCase
                     '$d' => 'array<int, int>',
                 ],
             ],
+            'printrOutput' => [
+                '<?php
+                    function foo(string $s) : void {
+                        echo $s;
+                    }
+
+                    foo(print_r(1, true));',
+            ],
         ];
     }