diff --git a/include/fc/io/json_relaxed.hpp b/include/fc/io/json_relaxed.hpp
index 2422db3..a3793a4 100644
--- a/include/fc/io/json_relaxed.hpp
+++ b/include/fc/io/json_relaxed.hpp
@@ -689,7 +689,7 @@ namespace fc { namespace json_relaxed
    {
       skip_white_space(in);
       variant var;
-      while( char c = in.peek() )
+      while( signed char c = in.peek() )
       {
          switch( c )
          {
diff --git a/src/io/json.cpp b/src/io/json.cpp
index 84446e1..b3f57cc 100644
--- a/src/io/json.cpp
+++ b/src/io/json.cpp
@@ -390,7 +390,7 @@ namespace fc
    {
       skip_white_space(in);
       variant var;
-      while( char c = in.peek() )
+      while( signed char c = in.peek() )
       {
          switch( c )
          {