diff --git a/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php b/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
index 52d62ecbb..d76f4db27 100644
--- a/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
+++ b/src/Psalm/Internal/Analyzer/Statements/Expression/AssertionFinder.php
@@ -1847,6 +1847,20 @@ class AssertionFinder
                             $if_types[$var_name] = [[$prefix . $assertion->rule[0][0]]];
                         }
                     }
+                } elseif ($assertion->var_id === '$this' && $expr instanceof PhpParser\Node\Expr\MethodCall) {
+                    $var_id = ExpressionAnalyzer::getArrayVarId(
+                        $expr->var,
+                        $this_class_name,
+                        $source
+                    );
+
+                    if ($var_id) {
+                        if ($prefix === $assertion->rule[0][0][0]) {
+                            $if_types[$var_id] = [[substr($assertion->rule[0][0], 1)]];
+                        } else {
+                            $if_types[$var_id] = [[$prefix . $assertion->rule[0][0]]];
+                        }
+                    }
                 }
             }
         }
@@ -1873,6 +1887,20 @@ class AssertionFinder
                             $if_types[$var_name] = [[$negated_prefix . $assertion->rule[0][0]]];
                         }
                     }
+                } elseif ($assertion->var_id === '$this' && $expr instanceof PhpParser\Node\Expr\MethodCall) {
+                    $var_id = ExpressionAnalyzer::getArrayVarId(
+                        $expr->var,
+                        $this_class_name,
+                        $source
+                    );
+
+                    if ($var_id) {
+                        if ($negated_prefix === $assertion->rule[0][0][0]) {
+                            $if_types[$var_id] = [[substr($assertion->rule[0][0], 1)]];
+                        } else {
+                            $if_types[$var_id] = [[$negated_prefix . $assertion->rule[0][0]]];
+                        }
+                    }
                 }
             }
         }
diff --git a/tests/AssertTest.php b/tests/AssertTest.php
index f57ab027c..cc6aaa0c7 100644
--- a/tests/AssertTest.php
+++ b/tests/AssertTest.php
@@ -956,6 +956,31 @@ class AssertTest extends TestCase
                         return $value;
                     }'
             ],
+            'assertThisTypeIfTrue' => [
+                '<?php
+                    class Type {
+                        /**
+                         * @psalm-assert-if-true FooType $this
+                         */
+                        public function isFoo() : bool {
+                            return $this instanceof FooType;
+                        }
+                    }
+
+                    class FooType extends Type {
+                        public function bar(): void {}
+                    }
+
+                    function takesType(Type $t) : void {
+                        if ($t->isFoo()) {
+                            $t->bar();
+                        }
+                        switch (true) {
+                            case $t->isFoo():
+                            $t->bar();
+                        }
+                    }'
+            ],
         ];
     }