diff --git a/javascript/extractor/src/com/semmle/js/ast/DefaultVisitor.java b/javascript/extractor/src/com/semmle/js/ast/DefaultVisitor.java
index cb11b9376ea..9e08063d361 100644
--- a/javascript/extractor/src/com/semmle/js/ast/DefaultVisitor.java
+++ b/javascript/extractor/src/com/semmle/js/ast/DefaultVisitor.java
@@ -97,8 +97,11 @@ public class DefaultVisitor<C, R> implements Visitor<C, R> {
   }
 
   @Override
-  public R visit(AssignmentPattern nd, C q) {
-    throw new CatastrophicError("Assignment patterns should not appear in the AST.");
+  public R visit(AssignmentPattern nd, C c) {
+    // assignment patterns should not appear in the AST, but can do for malformed
+    // programs; the ASTExtractor raises a ParseError in this case, other visitors
+    // should just ignore them
+    return visit(nd.getLeft(), c);
   }
 
   @Override
diff --git a/javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java b/javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java
index c2a1126070d..4bc7d0fbdd3 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/ASTExtractor.java
@@ -1,5 +1,11 @@
 package com.semmle.js.extractor;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Set;
+import java.util.Stack;
+
 import com.semmle.js.ast.AClass;
 import com.semmle.js.ast.AFunction;
 import com.semmle.js.ast.AFunctionExpression;
@@ -7,6 +13,7 @@ import com.semmle.js.ast.ArrayExpression;
 import com.semmle.js.ast.ArrayPattern;
 import com.semmle.js.ast.ArrowFunctionExpression;
 import com.semmle.js.ast.AssignmentExpression;
+import com.semmle.js.ast.AssignmentPattern;
 import com.semmle.js.ast.AwaitExpression;
 import com.semmle.js.ast.BinaryExpression;
 import com.semmle.js.ast.BindExpression;
@@ -103,6 +110,7 @@ import com.semmle.js.extractor.ExtractorConfig.Platform;
 import com.semmle.js.extractor.ExtractorConfig.SourceType;
 import com.semmle.js.extractor.ScopeManager.DeclKind;
 import com.semmle.js.extractor.ScopeManager.Scope;
+import com.semmle.js.parser.ParseError;
 import com.semmle.ts.ast.ArrayTypeExpr;
 import com.semmle.ts.ast.ConditionalTypeExpr;
 import com.semmle.ts.ast.DecoratorList;
@@ -144,11 +152,6 @@ import com.semmle.ts.ast.UnionTypeExpr;
 import com.semmle.util.collections.CollectionUtil;
 import com.semmle.util.trap.TrapWriter;
 import com.semmle.util.trap.TrapWriter.Label;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-import java.util.Set;
-import java.util.Stack;
 
 /** Extractor for AST-based information; invoked by the {@link JSExtractor}. */
 public class ASTExtractor {
@@ -307,6 +310,7 @@ public class ASTExtractor {
     private final Platform platform;
     private final SourceType sourceType;
     private boolean isStrict;
+    private List<ParseError> additionalErrors = new ArrayList<>();
 
     public V(Platform platform, SourceType sourceType) {
       this.platform = platform;
@@ -2054,14 +2058,22 @@ public class ASTExtractor {
       visit(nd.getRight(), key, 1, IdContext.label);
       return key;
     }
+
+    @Override
+    public Label visit(AssignmentPattern nd, Context c) {
+      additionalErrors.add(new ParseError("Unexpected assignment pattern.", nd.getLoc().getStart()));
+      return super.visit(nd, c);
+    }
   }
 
-  public void extract(Node root, Platform platform, SourceType sourceType, int toplevelKind) {
+  public List<ParseError> extract(Node root, Platform platform, SourceType sourceType, int toplevelKind) {
     lexicalExtractor.getMetrics().startPhase(ExtractionPhase.ASTExtractor_extract);
     trapwriter.addTuple("toplevels", toplevelLabel, toplevelKind);
     locationManager.emitNodeLocation(root, toplevelLabel);
 
-    root.accept(new V(platform, sourceType), null);
+    V visitor = new V(platform, sourceType);
+    root.accept(visitor, null);
     lexicalExtractor.getMetrics().stopPhase(ExtractionPhase.ASTExtractor_extract);
+    return visitor.additionalErrors;
   }
 }
diff --git a/javascript/extractor/src/com/semmle/js/extractor/JSExtractor.java b/javascript/extractor/src/com/semmle/js/extractor/JSExtractor.java
index 45dd4648220..2ce224b0225 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/JSExtractor.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/JSExtractor.java
@@ -113,7 +113,7 @@ public class JSExtractor {
       new JSDocExtractor(textualExtractor).extract(lexicalExtractor.getComments());
       lexicalExtractor.purge();
 
-      scriptExtractor.extract(ast, platform, sourceType, toplevelKind);
+      parserRes.getErrors().addAll(scriptExtractor.extract(ast, platform, sourceType, toplevelKind));
       new CFGExtractor(scriptExtractor).extract(ast);
     } else {
       lexicalExtractor =
diff --git a/javascript/extractor/src/com/semmle/js/extractor/Main.java b/javascript/extractor/src/com/semmle/js/extractor/Main.java
index 20016a0849d..4f522513873 100644
--- a/javascript/extractor/src/com/semmle/js/extractor/Main.java
+++ b/javascript/extractor/src/com/semmle/js/extractor/Main.java
@@ -37,7 +37,7 @@ public class Main {
    * A version identifier that should be updated every time the extractor changes in such a way that
    * it may produce different tuples for the same file under the same {@link ExtractorConfig}.
    */
-  public static final String EXTRACTOR_VERSION = "2019-11-26";
+  public static final String EXTRACTOR_VERSION = "2020-01-06";
 
   public static final Pattern NEWLINE = Pattern.compile("\n");
 
diff --git a/javascript/extractor/tests/errors/input/invalid-assignment-pattern.js b/javascript/extractor/tests/errors/input/invalid-assignment-pattern.js
new file mode 100644
index 00000000000..bfe2b3cd024
--- /dev/null
+++ b/javascript/extractor/tests/errors/input/invalid-assignment-pattern.js
@@ -0,0 +1 @@
+(x = 0) = y
diff --git a/javascript/extractor/tests/errors/output/trap/invalid-assignment-pattern.js.trap b/javascript/extractor/tests/errors/output/trap/invalid-assignment-pattern.js.trap
new file mode 100644
index 00000000000..858b3e94e70
--- /dev/null
+++ b/javascript/extractor/tests/errors/output/trap/invalid-assignment-pattern.js.trap
@@ -0,0 +1,117 @@
+#10000=@"/invalid-assignment-pattern.js;sourcefile"
+files(#10000,"/invalid-assignment-pattern.js","invalid-assignment-pattern","js",0)
+#10001=@"/;folder"
+folders(#10001,"/","")
+containerparent(#10001,#10000)
+#10002=@"loc,{#10000},0,0,0,0"
+locations_default(#10002,#10000,0,0,0,0)
+hasLocation(#10000,#10002)
+#20000=@"global_scope"
+scopes(#20000,0)
+#20001=@"script;{#10000},1,1"
+#20002=*
+lines(#20002,#20001,"(x = 0) = y","
+")
+#20003=@"loc,{#10000},1,1,1,11"
+locations_default(#20003,#10000,1,1,1,11)
+hasLocation(#20002,#20003)
+numlines(#20001,1,1,0)
+#20004=*
+tokeninfo(#20004,8,#20001,0,"(")
+#20005=@"loc,{#10000},1,1,1,1"
+locations_default(#20005,#10000,1,1,1,1)
+hasLocation(#20004,#20005)
+#20006=*
+tokeninfo(#20006,6,#20001,1,"x")
+#20007=@"loc,{#10000},1,2,1,2"
+locations_default(#20007,#10000,1,2,1,2)
+hasLocation(#20006,#20007)
+#20008=*
+tokeninfo(#20008,8,#20001,2,"=")
+#20009=@"loc,{#10000},1,4,1,4"
+locations_default(#20009,#10000,1,4,1,4)
+hasLocation(#20008,#20009)
+#20010=*
+tokeninfo(#20010,3,#20001,3,"0")
+#20011=@"loc,{#10000},1,6,1,6"
+locations_default(#20011,#10000,1,6,1,6)
+hasLocation(#20010,#20011)
+#20012=*
+tokeninfo(#20012,8,#20001,4,")")
+#20013=@"loc,{#10000},1,7,1,7"
+locations_default(#20013,#10000,1,7,1,7)
+hasLocation(#20012,#20013)
+#20014=*
+tokeninfo(#20014,8,#20001,5,"=")
+#20015=@"loc,{#10000},1,9,1,9"
+locations_default(#20015,#10000,1,9,1,9)
+hasLocation(#20014,#20015)
+#20016=*
+tokeninfo(#20016,6,#20001,6,"y")
+#20017=@"loc,{#10000},1,11,1,11"
+locations_default(#20017,#10000,1,11,1,11)
+hasLocation(#20016,#20017)
+#20018=*
+tokeninfo(#20018,0,#20001,7,"")
+#20019=@"loc,{#10000},2,1,2,0"
+locations_default(#20019,#10000,2,1,2,0)
+hasLocation(#20018,#20019)
+toplevels(#20001,0)
+#20020=@"loc,{#10000},1,1,2,0"
+locations_default(#20020,#10000,1,1,2,0)
+hasLocation(#20001,#20020)
+#20021=*
+stmts(#20021,2,#20001,0,"(x = 0) = y")
+hasLocation(#20021,#20003)
+stmtContainers(#20021,#20001)
+#20022=*
+exprs(#20022,47,#20021,0,"(x = 0) = y")
+hasLocation(#20022,#20003)
+enclosingStmt(#20022,#20021)
+exprContainers(#20022,#20001)
+#20023=*
+exprs(#20023,63,#20022,0,"(x = 0)")
+#20024=@"loc,{#10000},1,1,1,7"
+locations_default(#20024,#10000,1,1,1,7)
+hasLocation(#20023,#20024)
+enclosingStmt(#20023,#20021)
+exprContainers(#20023,#20001)
+#20025=*
+exprs(#20025,79,#20023,0,"x")
+hasLocation(#20025,#20007)
+enclosingStmt(#20025,#20021)
+exprContainers(#20025,#20001)
+#20026=*
+exprs(#20026,79,#20022,1,"y")
+hasLocation(#20026,#20017)
+enclosingStmt(#20026,#20021)
+exprContainers(#20026,#20001)
+literals("y","y",#20026)
+#20027=@"var;{y};{#20000}"
+variables(#20027,"y",#20000)
+bind(#20026,#20027)
+#20028=*
+entry_cfg_node(#20028,#20001)
+#20029=@"loc,{#10000},1,1,1,0"
+locations_default(#20029,#10000,1,1,1,0)
+hasLocation(#20028,#20029)
+#20030=*
+exit_cfg_node(#20030,#20001)
+hasLocation(#20030,#20019)
+successor(#20021,#20023)
+successor(#20026,#20022)
+successor(#20023,#20025)
+successor(#20025,#20026)
+successor(#20022,#20030)
+successor(#20028,#20021)
+#20031=*
+jsParseErrors(#20031,#20001,"Error: Unexpected assignment pattern.","(x = 0) = y
+")
+hasLocation(#20031,#20007)
+#20032=*
+lines(#20032,#20001,"(x = 0) = y","
+")
+hasLocation(#20032,#20003)
+numlines(#20001,1,0,0)
+numlines(#10000,1,1,0)
+filetype(#10000,"javascript")