diff --git a/flang-rt/include/flang-rt/runtime/format-implementation.h b/flang-rt/include/flang-rt/runtime/format-implementation.h
index de06524de32d3..46134146f5c13 100644
--- a/flang-rt/include/flang-rt/runtime/format-implementation.h
+++ b/flang-rt/include/flang-rt/runtime/format-implementation.h
@@ -532,7 +532,7 @@ RT_API_ATTRS common::optional<DataEdit> FormatControl<CONTEXT>::GetNextDataEdit(
           ReportBadFormat(context, "Excessive DT'iotype' in FORMAT", start);
           return common::nullopt;
         }
-        edit.ioType[edit.ioTypeChars++] = ch;
+        context.ioType[edit.ioTypeChars++] = ch;
         if (ch == quote) {
           ++offset_;
         }
@@ -556,7 +556,7 @@ RT_API_ATTRS common::optional<DataEdit> FormatControl<CONTEXT>::GetNextDataEdit(
           ReportBadFormat(context, "Excessive DT(v_list) in FORMAT", start);
           return common::nullopt;
         }
-        edit.vList[edit.vListEntries++] = n;
+        context.vList[edit.vListEntries++] = n;
         auto ch{static_cast<char>(GetNextChar(context))};
         if (ch != ',') {
           ok = ch == ')';
diff --git a/flang-rt/include/flang-rt/runtime/format.h b/flang-rt/include/flang-rt/runtime/format.h
index 34e33edae546d..79a7dd713b1a1 100644
--- a/flang-rt/include/flang-rt/runtime/format.h
+++ b/flang-rt/include/flang-rt/runtime/format.h
@@ -86,12 +86,11 @@ struct DataEdit {
   // defined I/O data edit descriptor
   RT_OFFLOAD_VAR_GROUP_BEGIN
   static constexpr std::size_t maxIoTypeChars{32};
-  static constexpr std::size_t maxVListEntries{4};
+  static constexpr std::size_t maxVListEntries{16};
   RT_OFFLOAD_VAR_GROUP_END
   std::uint8_t ioTypeChars{0};
   std::uint8_t vListEntries{0};
   char ioType[maxIoTypeChars];
-  int vList[maxVListEntries];
 };
 
 // Generates a sequence of DataEdits from a FORMAT statement or
diff --git a/flang-rt/include/flang-rt/runtime/io-stmt.h b/flang-rt/include/flang-rt/runtime/io-stmt.h
index 1c4f06c0a7082..21f152e082a21 100644
--- a/flang-rt/include/flang-rt/runtime/io-stmt.h
+++ b/flang-rt/include/flang-rt/runtime/io-stmt.h
@@ -61,8 +61,14 @@ using IoDirectionState = std::conditional_t<D == Direction::Input,
     InputStatementState, OutputStatementState>;
 
 // Common state for all kinds of formatted I/O
-template <Direction D> class FormattedIoStatementState {};
-template <> class FormattedIoStatementState<Direction::Input> {
+struct DefinedIoArgs {
+  char ioType[DataEdit::maxIoTypeChars]; // IOTYPE string
+  int vList[DataEdit::maxVListEntries]; // V_LIST(:) values
+};
+template <Direction D>
+class FormattedIoStatementState : public DefinedIoArgs {};
+template <>
+class FormattedIoStatementState<Direction::Input> : public DefinedIoArgs {
 public:
   RT_API_ATTRS std::size_t GetEditDescriptorChars() const;
   RT_API_ATTRS void GotChar(int);
diff --git a/flang-rt/lib/runtime/descriptor-io.cpp b/flang-rt/lib/runtime/descriptor-io.cpp
index e00072510aff7..4483906ecb508 100644
--- a/flang-rt/lib/runtime/descriptor-io.cpp
+++ b/flang-rt/lib/runtime/descriptor-io.cpp
@@ -62,10 +62,11 @@ static RT_API_ATTRS common::optional<bool> DefinedFormattedIo(
             : *io.GetNextDataEdit(1)};
     char ioType[2 + edit.maxIoTypeChars];
     auto ioTypeLen{std::size_t{2} /*"DT"*/ + edit.ioTypeChars};
+    auto &definedIoArgs{*io.get_if<DefinedIoArgs>()};
     if (edit.descriptor == DataEdit::DefinedDerivedType) {
       ioType[0] = 'D';
       ioType[1] = 'T';
-      runtime::memcpy(ioType + 2, edit.ioType, edit.ioTypeChars);
+      runtime::memcpy(ioType + 2, definedIoArgs.ioType, edit.ioTypeChars);
     } else {
       runtime::strcpy(
           ioType, io.mutableModes().inNamelist ? "NAMELIST" : "LISTDIRECTED");
@@ -79,7 +80,7 @@ static RT_API_ATTRS common::optional<bool> DefinedFormattedIo(
     if (integer8) {
       // Convert v_list values to INTEGER(8)
       for (int j{0}; j < edit.vListEntries; ++j) {
-        vList64[j] = edit.vList[j];
+        vList64[j] = definedIoArgs.vList[j];
       }
       vListDesc.Establish(
           TypeCategory::Integer, sizeof(std::int64_t), nullptr, 1);
@@ -89,7 +90,7 @@ static RT_API_ATTRS common::optional<bool> DefinedFormattedIo(
           static_cast<SubscriptValue>(sizeof(std::int64_t)));
     } else {
       vListDesc.Establish(TypeCategory::Integer, sizeof(int), nullptr, 1);
-      vListDesc.set_base_addr(edit.vList);
+      vListDesc.set_base_addr(definedIoArgs.vList);
       vListDesc.GetDimension(0).SetBounds(1, edit.vListEntries);
       vListDesc.GetDimension(0).SetByteStride(
           static_cast<SubscriptValue>(sizeof(int)));
diff --git a/flang-rt/unittests/Runtime/Format.cpp b/flang-rt/unittests/Runtime/Format.cpp
index fe7403f26700b..cd52dc8c54ed5 100644
--- a/flang-rt/unittests/Runtime/Format.cpp
+++ b/flang-rt/unittests/Runtime/Format.cpp
@@ -22,7 +22,7 @@ using namespace std::literals::string_literals;
 using ResultsTy = std::vector<std::string>;
 
 // A test harness context for testing FormatControl
-class TestFormatContext : public IoErrorHandler {
+class TestFormatContext : public IoErrorHandler, public DefinedIoArgs {
 public:
   using CharType = char;
   TestFormatContext() : IoErrorHandler{"format.cpp", 1} {}