diff --git a/include/etl/string.h b/include/etl/string.h
index 61101d06..677f0e5f 100644
--- a/include/etl/string.h
+++ b/include/etl/string.h
@@ -367,8 +367,9 @@ namespace etl
     /// Constructor, from null terminated text.
     ///\param text The initial text of the string_ext.
     //*************************************************************************
-    template <typename TPointer, typename = typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type>
-    string_ext(TPointer text, value_type* buffer, size_type buffer_size)
+    template <typename TPointer>
+    string_ext(TPointer text, value_type* buffer, size_type buffer_size,
+               typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type* = ETL_NULLPTR)
       : istring(buffer, buffer_size - 1U)
     {
       if (this->is_within_buffer(text))
diff --git a/include/etl/u16string.h b/include/etl/u16string.h
index 8da35cd0..69740e25 100644
--- a/include/etl/u16string.h
+++ b/include/etl/u16string.h
@@ -347,8 +347,9 @@ namespace etl
     /// Constructor, from null terminated text.
     ///\param text The initial text of the u16string_ext.
     //*************************************************************************
-    template <typename TPointer, typename = typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type>
-    u16string_ext(TPointer text, char* buffer, size_type buffer_size)
+    template <typename TPointer>
+    u16string_ext(TPointer text, value_type* buffer, size_type buffer_size,
+                  typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type* = ETL_NULLPTR)
       : iu16string(buffer, buffer_size - 1U)
     {
       if (this->is_within_buffer(text))
diff --git a/include/etl/u32string.h b/include/etl/u32string.h
index 17c49e06..a3120a25 100644
--- a/include/etl/u32string.h
+++ b/include/etl/u32string.h
@@ -347,8 +347,9 @@ namespace etl
     /// Constructor, from null terminated text.
     ///\param text The initial text of the u32string_ext.
     //*************************************************************************
-    template <typename TPointer, typename = typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type>
-    u32string_ext(TPointer text, char* buffer, size_type buffer_size)
+    template <typename TPointer>
+    u32string_ext(TPointer text, value_type* buffer, size_type buffer_size,
+                  typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type* = ETL_NULLPTR)
       : iu32string(buffer, buffer_size - 1U)
     {
       if (this->is_within_buffer(text))
diff --git a/include/etl/u8string.h b/include/etl/u8string.h
index 9aed486e..a64ee019 100644
--- a/include/etl/u8string.h
+++ b/include/etl/u8string.h
@@ -367,8 +367,9 @@ namespace etl
     /// Constructor, from null terminated text.
     ///\param text The initial text of the u8string_ext.
     //*************************************************************************
-    template <typename TPointer, typename = typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type>
-    u8string_ext(TPointer text, char* buffer, size_type buffer_size)
+    template <typename TPointer>
+    u8string_ext(TPointer text, value_type* buffer, size_type buffer_size,
+                 typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type* = ETL_NULLPTR)
       : iu8string(buffer, buffer_size - 1U)
     {
       if (this->is_within_buffer(text))
diff --git a/include/etl/wstring.h b/include/etl/wstring.h
index 157604f3..b17d45ac 100644
--- a/include/etl/wstring.h
+++ b/include/etl/wstring.h
@@ -347,8 +347,9 @@ namespace etl
     /// Constructor, from null terminated text.
     ///\param text The initial text of the wstring_ext.
     //*************************************************************************
-    template <typename TPointer, typename = typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type>
-    wstring_ext(TPointer text, char* buffer, size_type buffer_size)
+    template <typename TPointer>
+    wstring_ext(TPointer text, value_type* buffer, size_type buffer_size,
+                typename etl::enable_if<etl::is_same<const value_type*, TPointer>::value, int>::type* = ETL_NULLPTR)
       : iwstring(buffer, buffer_size - 1U)
     {
       if (this->is_within_buffer(text))