diff --git a/mlir/examples/toy/Ch1/include/toy/Parser.h b/mlir/examples/toy/Ch1/include/toy/Parser.h
--- a/mlir/examples/toy/Ch1/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch1/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch2/include/toy/Parser.h b/mlir/examples/toy/Ch2/include/toy/Parser.h
--- a/mlir/examples/toy/Ch2/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch2/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch3/include/toy/Parser.h b/mlir/examples/toy/Ch3/include/toy/Parser.h
--- a/mlir/examples/toy/Ch3/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch3/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch4/include/toy/Parser.h b/mlir/examples/toy/Ch4/include/toy/Parser.h
--- a/mlir/examples/toy/Ch4/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch4/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch5/include/toy/Parser.h b/mlir/examples/toy/Ch5/include/toy/Parser.h
--- a/mlir/examples/toy/Ch5/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch5/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch6/include/toy/Parser.h b/mlir/examples/toy/Ch6/include/toy/Parser.h
--- a/mlir/examples/toy/Ch6/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch6/include/toy/Parser.h
@@ -396,7 +396,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/examples/toy/Ch7/include/toy/Parser.h b/mlir/examples/toy/Ch7/include/toy/Parser.h
--- a/mlir/examples/toy/Ch7/include/toy/Parser.h
+++ b/mlir/examples/toy/Ch7/include/toy/Parser.h
@@ -534,7 +534,11 @@
   /// decl_list ::= identifier | identifier, decl_list
   std::unique_ptr<PrototypeAST> parsePrototype() {
     auto loc = lexer.getLastLocation();
+
+    if (lexer.getCurToken() != tok_def)
+      return parseError<PrototypeAST>("def", "in prototype");
     lexer.consume(tok_def);
+
     if (lexer.getCurToken() != tok_identifier)
       return parseError<PrototypeAST>("function name", "in prototype");
 
diff --git a/mlir/test/Examples/Toy/Ch1/empty.toy b/mlir/test/Examples/Toy/Ch1/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch1/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch1 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch2/empty.toy b/mlir/test/Examples/Toy/Ch2/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch2/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch2 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch3/empty.toy b/mlir/test/Examples/Toy/Ch3/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch3/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch3 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch4/empty.toy b/mlir/test/Examples/Toy/Ch4/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch4/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch4 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch5/empty.toy b/mlir/test/Examples/Toy/Ch5/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch5/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch5 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch6/empty.toy b/mlir/test/Examples/Toy/Ch6/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch6/empty.toy
@@ -0,0 +1,3 @@
+# RUN: toyc-ch6 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK: Parse error
diff --git a/mlir/test/Examples/Toy/Ch7/empty.toy b/mlir/test/Examples/Toy/Ch7/empty.toy
new file mode 100644
--- /dev/null
+++ b/mlir/test/Examples/Toy/Ch7/empty.toy
@@ -0,0 +1,4 @@
+# RUN: toyc-ch7 %s -emit=ast 2>&1 | FileCheck %s
+# CHECK-NOT: Assert
+# CHECK-NOT: Parse error
+# CHECK: Module