diff --git a/src/emitterutils.cpp b/src/emitterutils.cpp
index c6ad5e5..6cdf6de 100644
--- a/src/emitterutils.cpp
+++ b/src/emitterutils.cpp
@@ -176,11 +176,11 @@ bool IsValidPlainScalar(const std::string& str, FlowType::value flowType,
   static const RegEx& disallowed_flow =
       Exp::EndScalarInFlow() | (Exp::BlankOrBreak() + Exp::Comment()) |
       Exp::NotPrintable() | Exp::Utf8_ByteOrderMark() | Exp::Break() |
-      Exp::Tab();
+      Exp::Tab() | Exp::Ampersand();
   static const RegEx& disallowed_block =
       Exp::EndScalar() | (Exp::BlankOrBreak() + Exp::Comment()) |
       Exp::NotPrintable() | Exp::Utf8_ByteOrderMark() | Exp::Break() |
-      Exp::Tab();
+      Exp::Tab() | Exp::Ampersand();
   const RegEx& disallowed =
       flowType == FlowType::Flow ? disallowed_flow : disallowed_block;
 
diff --git a/src/exp.h b/src/exp.h
index a0d6d76..c8837f0 100644
--- a/src/exp.h
+++ b/src/exp.h
@@ -117,6 +117,10 @@ inline const RegEx& ValueInJSONFlow() {
   static const RegEx e = RegEx(':');
   return e;
 }
+inline const RegEx& Ampersand() {
+  static const RegEx e = RegEx('&');
+  return e;
+}
 inline const RegEx Comment() {
   static const RegEx e = RegEx('#');
   return e;