diff --git a/mlir/lib/Tools/PDLL/Parser/Lexer.h b/mlir/lib/Tools/PDLL/Parser/Lexer.h
--- a/mlir/lib/Tools/PDLL/Parser/Lexer.h
+++ b/mlir/lib/Tools/PDLL/Parser/Lexer.h
@@ -206,6 +206,7 @@
 
   /// Lex methods.
   void lexComment();
+  LogicalResult lexCComment();
   Token lexDirective(const char *tokStart);
   Token lexIdentifier(const char *tokStart);
   Token lexNumber(const char *tokStart);
diff --git a/mlir/lib/Tools/PDLL/Parser/Lexer.cpp b/mlir/lib/Tools/PDLL/Parser/Lexer.cpp
--- a/mlir/lib/Tools/PDLL/Parser/Lexer.cpp
+++ b/mlir/lib/Tools/PDLL/Parser/Lexer.cpp
@@ -235,6 +235,10 @@
         if (*curPtr == '/') {
           lexComment();
           continue;
+        } else if (*curPtr == '*') {
+          if (failed(lexCComment()))
+            return emitError(curPtr - 1, "unterminated comment");
+          continue;
         }
         return emitError(tokStart, "unexpected character");
 
@@ -291,6 +295,38 @@
   }
 }
 
+/// Skip a c-style comment, which is in the form of /**/.
+LogicalResult Lexer::lexCComment() {
+  // Advance over the '*'.
+  assert(*curPtr == '*');
+  ++curPtr;
+  unsigned nestedDepth = 1;
+
+  while (true) {
+    switch (*curPtr++) {
+    case 0:
+      return failure();
+    case '*':
+      if (curPtr[0] == '/') {
+        // This is the end of comment.
+        ++curPtr;
+        if (--nestedDepth == 0)
+          return success();
+      }
+      break;
+    case '/':
+      if (curPtr[0] == '*') {
+        // Start of a nested comment.
+        ++nestedDepth;
+        ++curPtr;
+      }
+      break;
+    }
+  }
+
+  llvm_unreachable("EOF is handled in the switch above");
+}
+
 Token Lexer::lexDirective(const char *tokStart) {
   // Match the rest with an identifier regex: [0-9a-zA-Z_]*
   while (isalnum(*curPtr) || *curPtr == '_') ++curPtr;
diff --git a/mlir/test/mlir-pdll/Parser/comment-failure.pdll b/mlir/test/mlir-pdll/Parser/comment-failure.pdll
new file mode 100644
--- /dev/null
+++ b/mlir/test/mlir-pdll/Parser/comment-failure.pdll
@@ -0,0 +1,8 @@
+// RUN: not mlir-pdll %s -I %S -split-input-file 2>&1 | FileCheck %s
+
+/*
+  /* This is malformed C-style comment */
+// CHECK: unterminated comment
+Pattern {
+  erase _: Op;
+}
diff --git a/mlir/test/mlir-pdll/Parser/comment.pdll b/mlir/test/mlir-pdll/Parser/comment.pdll
new file mode 100644
--- /dev/null
+++ b/mlir/test/mlir-pdll/Parser/comment.pdll
@@ -0,0 +1,33 @@
+// RUN: mlir-pdll %s -I %S -split-input-file 2>&1 | FileCheck %s
+
+/* This is C-style comment in single line */
+// CHECK: Module
+// CHECK: EraseStmt
+// CHECK:   `-DeclRefExpr {{.*}} Type<Op>
+Pattern {
+  erase _: Op;
+}
+
+// -----
+
+/*
+  This is C-style comment in multiple lines
+*/
+// CHECK: Module
+// CHECK: EraseStmt
+// CHECK:   `-DeclRefExpr {{.*}} Type<Op>
+Pattern {
+  erase _: Op;
+}
+
+// -----
+
+/*
+  /* This is nested C-style comment in multiple lines */
+*/
+// CHECK: Module
+// CHECK: EraseStmt
+// CHECK:   `-DeclRefExpr {{.*}} Type<Op>
+Pattern {
+  erase _: Op;
+}