diff --git a/src/preprocessor.cpp b/src/preprocessor.cpp
index ed56198d6..a65b5eb1b 100644
--- a/src/preprocessor.cpp
+++ b/src/preprocessor.cpp
@@ -262,7 +262,7 @@ std::string Preprocessor::read(std::istream &istr)
             ++lineno;
 
         // Replace assorted special chars with spaces..
-        if ((ch != '\n') && (std::isspace(ch) || std::iscntrl(ch)))
+        if ((ch > 0) && (ch != '\n') && (std::isspace(ch) || std::iscntrl(ch)))
             ch = ' ';
 
         // Skip spaces after ' ' and after '#'
@@ -274,7 +274,7 @@ std::string Preprocessor::read(std::istream &istr)
         {
             if (ch == '(')
                 code << " ";
-            else if (! std::isalpha(ch))
+            else if ((ch > 0) && ! std::isalpha(ch))
                 needSpace = false;
         }
         if (ch == '#')
@@ -287,7 +287,7 @@ std::string Preprocessor::read(std::istream &istr)
             while (true)
             {
                 chNext = (char)istr.peek();
-                if (chNext != '\n' && chNext != '\r' &&
+                if (chNext != '\n' && chNext != '\r' && (chNext > 0) &&
                     (std::isspace(chNext) || std::iscntrl(chNext)))
                 {
                     // Skip whitespace between <backspace> and <newline>
diff --git a/test/testpreprocessor.cpp b/test/testpreprocessor.cpp
index 73d5470ab..56beff398 100644
--- a/test/testpreprocessor.cpp
+++ b/test/testpreprocessor.cpp
@@ -126,7 +126,9 @@ private:
         TEST_CASE(endifsemicolon);
         TEST_CASE(missing_doublequote);
 
-        TEST_CASE(unicode1);
+        TEST_CASE(unicodeInCode);
+        TEST_CASE(unicodeInComment);
+        TEST_CASE(unicodeInString);
         TEST_CASE(define_part_of_func);
         TEST_CASE(conditionalDefine);
         TEST_CASE(multiline_comment);
@@ -996,13 +998,28 @@ private:
         }
     }
 
-    void unicode1()
+    void unicodeInCode()
     {
-        const char filedata[] = {'a', (char)200, 0};
+        const std::string filedata(std::string("a") + char(200));
         std::istringstream istr(filedata);
         ASSERT_THROW(Preprocessor::read(istr), std::runtime_error);
     }
 
+    void unicodeInComment()
+    {
+        const std::string filedata(std::string("//") + char(200));
+        std::istringstream istr(filedata.c_str());
+        ASSERT_EQUALS("", Preprocessor::read(istr));
+    }
+
+    void unicodeInString()
+    {
+        const std::string filedata(std::string("\"") + char(200) + "\"");
+        std::istringstream istr(filedata.c_str());
+        ASSERT_EQUALS(filedata, Preprocessor::read(istr));
+    }
+
+
     void define_part_of_func()
     {
         errout.str("");