diff --git a/dmd/mars.h b/dmd/mars.h
index 6db42544..8d45ff40 100644
--- a/dmd/mars.h
+++ b/dmd/mars.h
@@ -133,13 +133,15 @@ enum OS
     OSSolaris,
 };
 
+typedef unsigned char ubyte;
+
 // Put command line switches in here
 struct Param
 {
     bool obj;           // write object file
     bool link;          // perform link
     bool verbose;       // verbose compile
-    char symdebug;	// insert debug symbolic information
+    ubyte symdebug;	// insert debug symbolic information
 #if !IN_LLVM
     // LDC uses a different mechanism
     bool optimize;      // run optimizer
@@ -159,7 +161,7 @@ struct Param
     bool useUnitTests;  // generate unittest code
     bool useInline;     // inline expand functions
     bool warnings;      // enable warnings
-    char Dversion;	// D version number
+    ubyte Dversion;	// D version number
     char safe;		// enforce safe memory model
 
     char *argv0;	// program name
diff --git a/gen/cl_options.cpp b/gen/cl_options.cpp
index c6d95bc7..b8318ad9 100644
--- a/gen/cl_options.cpp
+++ b/gen/cl_options.cpp
@@ -25,7 +25,7 @@ static cl::opt<bool, true> useDeprecated("d",
     cl::ZeroOrMore,
     cl::location(global.params.useDeprecated));
 
-static cl::opt<char, true> useDv1(
+static cl::opt<ubyte, true> useDv1(
     cl::desc("Force language version:"),
     cl::ZeroOrMore,
     cl::values(
@@ -49,7 +49,7 @@ static cl::opt<bool, true> warnings("w",
     cl::ZeroOrMore,
     cl::location(global.params.warnings));
 
-static cl::opt<char, true> debugInfo(
+static cl::opt<ubyte, true> debugInfo(
     cl::desc("Generating debug information:"),
     cl::ZeroOrMore,
     cl::values(
diff --git a/gen/optimizer.cpp b/gen/optimizer.cpp
index a825dc4a..522346a3 100644
--- a/gen/optimizer.cpp
+++ b/gen/optimizer.cpp
@@ -21,7 +21,7 @@ static cl::list<const PassInfo*, bool, PassNameParser>
         cl::Hidden      // to clean up --help output
     );
 
-static cl::opt<char> optimizeLevel(
+static cl::opt<unsigned char> optimizeLevel(
     cl::desc("Setting the optimization level:"),
     cl::ZeroOrMore,
     cl::values(