diff --git a/src/Psalm/Checker/Statements/Block/IfChecker.php b/src/Psalm/Checker/Statements/Block/IfChecker.php
index a7a99afaa..0e70f0fe2 100644
--- a/src/Psalm/Checker/Statements/Block/IfChecker.php
+++ b/src/Psalm/Checker/Statements/Block/IfChecker.php
@@ -180,7 +180,7 @@ class IfChecker
 
         $if_context->inside_conditional = false;
 
-        $mixed_var_ids = [];
+        $mixed_var_ids = ['$_GET', '$_POST'];
 
         foreach ($if_context->vars_in_scope as $var_id => $type) {
             if ($type->isMixed()) {
@@ -871,7 +871,7 @@ class IfChecker
 
         $elseif_context->inside_conditional = false;
 
-        $mixed_var_ids = [];
+        $mixed_var_ids = ['$_GET', '$_POST'];
 
         foreach ($elseif_context->vars_in_scope as $var_id => $type) {
             if ($type->isMixed()) {
diff --git a/src/Psalm/Checker/Statements/Expression/BinaryOpChecker.php b/src/Psalm/Checker/Statements/Expression/BinaryOpChecker.php
index 5659a746d..1a9fa88fb 100644
--- a/src/Psalm/Checker/Statements/Expression/BinaryOpChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/BinaryOpChecker.php
@@ -283,7 +283,7 @@ class BinaryOpChecker
                 $statements_checker
             );
 
-            $mixed_var_ids = [];
+            $mixed_var_ids = ['$_GET', '$_POST'];
 
             foreach ($context->vars_in_scope as $var_id => $type) {
                 if ($type->isMixed()) {
diff --git a/src/Psalm/Checker/Statements/Expression/TernaryChecker.php b/src/Psalm/Checker/Statements/Expression/TernaryChecker.php
index 4f6ea38fc..936c04397 100644
--- a/src/Psalm/Checker/Statements/Expression/TernaryChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/TernaryChecker.php
@@ -45,6 +45,43 @@ class TernaryChecker
             $statements_checker
         );
 
+        $mixed_var_ids = ['$_GET', '$_POST'];
+
+        foreach ($context->vars_in_scope as $var_id => $type) {
+            if ($type->isMixed()) {
+                $mixed_var_ids[] = $var_id;
+            }
+        }
+
+        foreach ($context->vars_possibly_in_scope as $var_id => $_) {
+            if (!isset($context->vars_in_scope[$var_id])) {
+                $mixed_var_ids[] = $var_id;
+            }
+        }
+
+
+        $if_clauses = array_values(
+            array_map(
+                /**
+                 * @return \Psalm\Clause
+                 */
+                function (\Psalm\Clause $c) use ($mixed_var_ids) {
+                    $keys = array_keys($c->possibilities);
+
+                    foreach ($keys as $key) {
+                        foreach ($mixed_var_ids as $mixed_var_id) {
+                            if (preg_match('/^' . preg_quote($mixed_var_id, '/') . '(\[|-)/', $key)) {
+                                return new \Psalm\Clause([], true);
+                            }
+                        }
+                    }
+
+                    return $c;
+                },
+                $if_clauses
+            )
+        );
+
         $ternary_clauses = Algebra::simplifyCNF(array_merge($context->clauses, $if_clauses));
 
         $negated_clauses = Algebra::negateFormula($if_clauses);
diff --git a/src/Psalm/Checker/StatementsChecker.php b/src/Psalm/Checker/StatementsChecker.php
index d06cdc05d..93beb12b2 100644
--- a/src/Psalm/Checker/StatementsChecker.php
+++ b/src/Psalm/Checker/StatementsChecker.php
@@ -1055,7 +1055,7 @@ class StatementsChecker extends SourceChecker implements StatementsSource
             return $context->vars_in_scope[$const_name];
         }
 
-        $file_path = $statements_checker->getFilePath();
+        $file_path = $statements_checker->getRootFilePath();
         $project_checker = $statements_checker->getFileChecker()->project_checker;
 
         $file_storage_provider = $project_checker->file_storage_provider;
diff --git a/tests/IssetTest.php b/tests/IssetTest.php
index 35c5a575b..7d6d2744b 100644
--- a/tests/IssetTest.php
+++ b/tests/IssetTest.php
@@ -334,6 +334,13 @@ class IssetTest extends TestCase
                         if ($arr[$k][0]) {}
                     }',
             ],
+            'mixedArrayIsset' => [
+                '<?php
+                    $a = isset($_GET["a"]) ? $_GET["a"] : "";
+                    if ($a) {}',
+                'assertions' => [],
+                'error_levels' => ['MixedAssignment', 'MixedArrayAccess'],
+            ],
         ];
     }