diff --git a/headers/os/support/String.h b/headers/os/support/String.h
index 005fcd219a..4ce0d13729 100644
--- a/headers/os/support/String.h
+++ b/headers/os/support/String.h
@@ -6,10 +6,11 @@
 #define __BSTRING__
 
 
-#include <BeBuild.h>
-#include <SupportDefs.h>
+#include <stdarg.h>
 #include <string.h>
 
+#include <SupportDefs.h>
+
 
 class BStringList;
 class BStringRef;
@@ -55,6 +56,8 @@ public:
 			BString&		AdoptChars(BString& from, int32 charCount);
 
 			BString&		SetToFormat(const char* format, ...);
+			BString&		SetToFormatVarArgs(const char* format,
+								va_list args);
 
 			// Substring copying
 			BString&		CopyInto(BString& into, int32 fromOffset,
diff --git a/src/kits/support/String.cpp b/src/kits/support/String.cpp
index 7bc0751d56..e29e082464 100644
--- a/src/kits/support/String.cpp
+++ b/src/kits/support/String.cpp
@@ -428,13 +428,31 @@ BString::AdoptChars(BString& string, int32 charCount)
 BString&
 BString::SetToFormat(const char* format, ...)
 {
+	va_list args;
+	va_start(args, format);
+	SetToFormatVarArgs(format, args);
+	va_end(args);
+
+	return *this;
+}
+
+
+BString&
+BString::SetToFormatVarArgs(const char* format, va_list args)
+{
+	// Use a small on-stack buffer to save a second vsnprintf() call for most
+	// use cases.
 	int32 bufferSize = 1024;
 	char buffer[bufferSize];
 
-	va_list arg;
-	va_start(arg, format);
-	int32 bytes = vsnprintf(buffer, bufferSize, format, arg);
-	va_end(arg);
+	va_list clonedArgs;
+#if __GNUC__ == 2
+	__va_copy(clonedArgs, args);
+#else
+	va_copy(clonedArgs, args);
+#endif
+	int32 bytes = vsnprintf(buffer, bufferSize, format, clonedArgs);
+	va_end(clonedArgs);
 
 	if (bytes < 0)
 		return Truncate(0);
@@ -444,11 +462,7 @@ BString::SetToFormat(const char* format, ...)
 		return *this;
 	}
 
-	va_list arg2;
-	va_start(arg2, format);
-	bytes = vsnprintf(LockBuffer(bytes), bytes + 1, format, arg2);
-	va_end(arg2);
-
+	bytes = vsnprintf(LockBuffer(bytes), bytes + 1, format, args);
 	if (bytes < 0)
 		bytes = 0;