diff --git a/JsonGeneratorTests/StringBuilder.cpp b/JsonGeneratorTests/StringBuilder.cpp
index d9e3167a..af4b2b98 100644
--- a/JsonGeneratorTests/StringBuilder.cpp
+++ b/JsonGeneratorTests/StringBuilder.cpp
@@ -10,9 +10,12 @@ void StringBuilder::append(const char* s)
 {
     char* tail = buffer + length;
 
-    strncpy(tail, s, capacity - length);
+    while (*s && length<capacity)
+    {
+        buffer[length++] = *s++;
+    }
 
-    length += strlen(tail);
+    buffer[length] = 0;
 }
 
 void StringBuilder::appendEscaped(const char* s)
@@ -24,7 +27,7 @@ void StringBuilder::appendEscaped(const char* s)
     // keep one slot for the end quote
     capacity--;
 
-    while (*s && length<capacity)
+    while (*s && length < capacity)
     {
         switch (*s)
         {
diff --git a/JsonGeneratorTests/StringBuilder.h b/JsonGeneratorTests/StringBuilder.h
index d47a8602..1747eb6c 100644
--- a/JsonGeneratorTests/StringBuilder.h
+++ b/JsonGeneratorTests/StringBuilder.h
@@ -13,7 +13,7 @@ class StringBuilder
 {
 public:
     StringBuilder(char* buf, size_t size)
-        : buffer(buf), capacity(size), length(0)
+        : buffer(buf), capacity(size-1), length(0)
     {
         buffer[0] = 0;
     }
@@ -24,7 +24,7 @@ public:
 
 private:
     char* buffer;
-    int capacity;
-    int length;
+    size_t capacity;
+    size_t length;
 };
 
diff --git a/JsonGeneratorTests/StringBuilderTests.cpp b/JsonGeneratorTests/StringBuilderTests.cpp
index b89705e5..cf0823be 100644
--- a/JsonGeneratorTests/StringBuilderTests.cpp
+++ b/JsonGeneratorTests/StringBuilderTests.cpp
@@ -42,6 +42,12 @@ namespace JsonGeneratorTests
             assertResultIs("ABCDEFGH");
         }
 
+        TEST_METHOD(AppendOverCapacity)
+        {
+            append("ABCDEFGHIJKLMNOPQRSTUVWXYZ");
+            assertResultIs("ABCDEFGHIJKLMNO");
+        }
+
         TEST_METHOD(AppendSpecialChars)
         {
             append("\\\"\/\b\f\n\r");