diff --git a/src/Psalm/Internal/Codebase/ClassLikes.php b/src/Psalm/Internal/Codebase/ClassLikes.php
index 61cd57daf..8654a213b 100644
--- a/src/Psalm/Internal/Codebase/ClassLikes.php
+++ b/src/Psalm/Internal/Codebase/ClassLikes.php
@@ -298,7 +298,7 @@ class ClassLikes
         $fq_class_name_lc = strtolower($fq_class_name);
 
         if (isset($this->classlike_aliases[$fq_class_name_lc])) {
-            $fq_class_name_lc = $this->classlike_aliases[$fq_class_name_lc];
+            $fq_class_name_lc = strtolower($this->classlike_aliases[$fq_class_name_lc]);
         }
 
         if (!isset($this->existing_interfaces_lc[$fq_class_name_lc])
@@ -344,7 +344,7 @@ class ClassLikes
         $fq_class_name_lc = strtolower($fq_class_name);
 
         if (isset($this->classlike_aliases[$fq_class_name_lc])) {
-            $fq_class_name_lc = $this->classlike_aliases[$fq_class_name_lc];
+            $fq_class_name_lc = strtolower($this->classlike_aliases[$fq_class_name_lc]);
         }
 
         if (!isset($this->existing_traits_lc[$fq_class_name_lc]) ||
@@ -559,6 +559,10 @@ class ClassLikes
             return true;
         }
 
+        if (isset($this->classlike_aliases[strtolower($fq_interface_name)])) {
+            return true;
+        }
+
         return isset($this->existing_interfaces[$fq_interface_name]);
     }
 
diff --git a/src/Psalm/Internal/Codebase/Populator.php b/src/Psalm/Internal/Codebase/Populator.php
index 996fb1a75..1f2b7bdaf 100644
--- a/src/Psalm/Internal/Codebase/Populator.php
+++ b/src/Psalm/Internal/Codebase/Populator.php
@@ -289,6 +289,9 @@ class Populator
     ) {
         foreach ($storage->used_traits as $used_trait_lc => $_) {
             try {
+                $used_trait_lc = $this->classlikes->getUnAliasedName(
+                    $used_trait_lc
+                );
                 $trait_storage = $storage_provider->get($used_trait_lc);
             } catch (\InvalidArgumentException $e) {
                 continue;
@@ -312,6 +315,9 @@ class Populator
         $parent_storage_class = reset($storage->parent_classes);
 
         try {
+            $parent_storage_class = $this->classlikes->getUnAliasedName(
+                strtolower($parent_storage_class)
+            );
             $parent_storage = $storage_provider->get($parent_storage_class);
         } catch (\InvalidArgumentException $e) {
             $storage->invalid_dependencies[] = $parent_storage_class;
@@ -364,6 +370,9 @@ class Populator
 
         foreach ($storage->parent_interfaces as $parent_interface_lc => $_) {
             try {
+                $parent_interface_lc = $this->classlikes->getUnAliasedName(
+                    $parent_interface_lc
+                );
                 $parent_interface_storage = $storage_provider->get($parent_interface_lc);
             } catch (\InvalidArgumentException $e) {
                 $storage->invalid_dependencies[] = $parent_interface_lc;
@@ -403,6 +412,9 @@ class Populator
 
         foreach ($storage->class_implements as $implemented_interface_lc => $_) {
             try {
+                $implemented_interface_lc = $this->classlikes->getUnAliasedName(
+                    strtolower($implemented_interface_lc)
+                );
                 $implemented_interface_storage = $storage_provider->get($implemented_interface_lc);
             } catch (\InvalidArgumentException $e) {
                 $storage->invalid_dependencies[] = $implemented_interface_lc;
@@ -431,6 +443,9 @@ class Populator
 
         foreach ($storage->class_implements as $implemented_interface) {
             try {
+                $implemented_interface = $this->classlikes->getUnAliasedName(
+                    strtolower($implemented_interface)
+                );
                 $implemented_interface_storage = $storage_provider->get($implemented_interface);
             } catch (\InvalidArgumentException $e) {
                 continue;
diff --git a/src/Psalm/Internal/Codebase/Scanner.php b/src/Psalm/Internal/Codebase/Scanner.php
index c5fde4904..43f7349ff 100644
--- a/src/Psalm/Internal/Codebase/Scanner.php
+++ b/src/Psalm/Internal/Codebase/Scanner.php
@@ -721,7 +721,7 @@ class Scanner
         $new_fq_class_name = $reflected_class->getName();
 
         if (strtolower($new_fq_class_name) !== strtolower($fq_class_name)) {
-            $classlikes->addClassAlias($new_fq_class_name, $fq_class_name);
+            $classlikes->addClassAlias($new_fq_class_name, strtolower($fq_class_name));
         }
 
         $fq_class_name = $new_fq_class_name;
diff --git a/tests/StubTest.php b/tests/StubTest.php
index ad2907394..78db18712 100644
--- a/tests/StubTest.php
+++ b/tests/StubTest.php
@@ -369,7 +369,9 @@ class StubTest extends TestCase
                     return f();
                 }
 
-                $d = new D();'
+                $d = new D();
+
+                class E implements IAlias {}'
         );
 
         $this->analyzeFile($file_path, new Context());
diff --git a/tests/stubs/class_alias.php b/tests/stubs/class_alias.php
index fe0a6b9b3..9ae353f9c 100644
--- a/tests/stubs/class_alias.php
+++ b/tests/stubs/class_alias.php
@@ -13,12 +13,17 @@ class A {
     }
 }
 
+interface I {}
+
 class_alias("ClassAliasStubTest\\A", "ClassAliasStubTest\\B");
 class_alias(A::class, C::class);
 
 $arr = [
-    [A::class, D::class]
+    [A::class, D::class],
+    [I::class, IAlias::class],
 ];
 
-// Psalm cannot reason about this in the loading step
-class_alias($arr[0][0], $arr[0][1]);
+foreach ($arr as list($orig, $alias)) {
+    // Psalm cannot reason about this in the loading step
+    class_alias($orig, $alias);
+}