diff --git a/ASTree.cpp b/ASTree.cpp
index a0c35939..a04852c9 100644
--- a/ASTree.cpp
+++ b/ASTree.cpp
@@ -620,6 +620,16 @@ PycRef<ASTNode> BuildFromCode(PycRef<PycCode> code, PycModule* mod)
                 stack.push(new ASTCompare(left, right, operand));
             }
             break;
+        case Pyc::CONTAINS_OP_A:
+            {
+                PycRef<ASTNode> right = stack.top();
+                stack.pop();
+                PycRef<ASTNode> left = stack.top();
+                stack.pop();
+                // The operand will be 0 for 'in' and 1 for 'not in'.
+                stack.push(new ASTCompare(left, right, operand ? ASTCompare::CMP_NOT_IN : ASTCompare::CMP_IN));
+            }
+            break;
         case Pyc::DELETE_ATTR_A:
             {
                 PycRef<ASTNode> name = stack.top();
diff --git a/tests/compiled/contains_op.3.9.pyc b/tests/compiled/contains_op.3.9.pyc
new file mode 100644
index 00000000..78b9c181
Binary files /dev/null and b/tests/compiled/contains_op.3.9.pyc differ
diff --git a/tests/input/contains_op.py b/tests/input/contains_op.py
new file mode 100644
index 00000000..c4b207ab
--- /dev/null
+++ b/tests/input/contains_op.py
@@ -0,0 +1,8 @@
+a = 10
+b = [10, 20, 30]
+
+if a in b:
+    pass
+
+if a not in b:
+    pass
diff --git a/tests/tokenized/contains_op.txt b/tests/tokenized/contains_op.txt
new file mode 100644
index 00000000..f33e0931
--- /dev/null
+++ b/tests/tokenized/contains_op.txt
@@ -0,0 +1,9 @@
+a = 10 <EOL>
+b = [ 10 , 20 , 30 ] <EOL>
+if a in b : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+if a not in b : <EOL>
+<INDENT>
+pass <EOL>