diff --git a/packages/babel-parser/src/parser/expression.js b/packages/babel-parser/src/parser/expression.js
index 51156faed2..d234a72e21 100644
--- a/packages/babel-parser/src/parser/expression.js
+++ b/packages/babel-parser/src/parser/expression.js
@@ -1227,6 +1227,26 @@ export default class ExpressionParser extends LValParser {
         return node;
       }
 
+      case tt.moduloAssign:
+        if (
+          this.getPluginOption("pipelineOperator", "proposal") === "hack" &&
+          this.getPluginOption("pipelineOperator", "topicToken") === "%"
+        ) {
+          // If we find %= in an expression position, and the Hack-pipes proposal is active,
+          // then the % could be the topic token (e.g., in x |> %==y or x |> %===y), and so we
+          // reparse it as %.
+          // The next readToken() call will start parsing from =.
+
+          this.state.value = "%";
+          this.state.type = tt.modulo;
+          this.state.pos--;
+          this.state.end--;
+          this.state.endLoc.column--;
+        } else {
+          throw this.unexpected();
+        }
+
+      // falls through
       case tt.modulo:
       case tt.hash: {
         const pipeProposal = this.getPluginOption(
diff --git a/packages/babel-parser/src/tokenizer/index.js b/packages/babel-parser/src/tokenizer/index.js
index a11c916499..0894adf143 100644
--- a/packages/babel-parser/src/tokenizer/index.js
+++ b/packages/babel-parser/src/tokenizer/index.js
@@ -615,7 +615,7 @@ export default class Tokenizer extends ParserErrors {
 
     if (next === charCodes.equalsTo && !this.state.inType) {
       width++;
-      type = tt.assign;
+      type = code === charCodes.percentSign ? tt.moduloAssign : tt.assign;
     }
 
     this.finishOp(type, width);
diff --git a/packages/babel-parser/src/tokenizer/types.js b/packages/babel-parser/src/tokenizer/types.js
index 6b394ba4db..9188b7b4aa 100644
--- a/packages/babel-parser/src/tokenizer/types.js
+++ b/packages/babel-parser/src/tokenizer/types.js
@@ -140,6 +140,9 @@ export const types: { [name: string]: TokenType } = {
   eq: new TokenType("=", { beforeExpr, isAssign }),
   assign: new TokenType("_=", { beforeExpr, isAssign }),
   slashAssign: new TokenType("_=", { beforeExpr, isAssign }),
+  // This is only needed to support % as a Hack-pipe topic token. If the proposal
+  // ends up choosing a different token, it can be merged with tt.assign.
+  moduloAssign: new TokenType("_=", { beforeExpr, isAssign }),
   incDec: new TokenType("++/--", { prefix, postfix, startsExpr }),
   bang: new TokenType("!", { beforeExpr, prefix, startsExpr }),
   tilde: new TokenType("~", { beforeExpr, prefix, startsExpr }),