diff --git a/autotest/StreamUTF8Test/StreamUTF8Test.cpp b/autotest/StreamUTF8Test/StreamUTF8Test.cpp
new file mode 100644
index 000000000..c7612e0de
--- /dev/null
+++ b/autotest/StreamUTF8Test/StreamUTF8Test.cpp
@@ -0,0 +1,38 @@
+#include <Core/Core.h>
+
+using namespace Upp;
+
+void ValidateUtf8(const String& src, int begin, int end, int pos)
+{
+	// Checks for malformed, imcomplete and overlong UTF-8 sequences.
+	// Replaces each malformed/illegal byte with the replacement character. (Recommended method)
+	// The length of the original line and decoded/replated line MUST be equal for these sequences.
+	
+	String dest;
+	StringStream ss(src);
+	bool check_utf8 = pos >= begin && pos < end;
+	while(!ss.IsEof()) {
+		int c = check_utf8 ? ss.GetUtf8() : ss.Get();
+		dest.Cat(c < 0 ? 0xFFFD : c);
+	}
+	DLOG(dest);
+	if(check_utf8)
+		ASSERT(dest.GetLength() == src.GetLength());
+}
+
+CONSOLE_APP_MAIN
+{
+	// This autotest uses Marcus Kuhn's UTf-8 stress test text.
+	// StdLogSetup(LOG_COUT);
+	String text = LoadDataFile("utf8_stress_test.txt");
+	ASSERT(!IsNull(text));
+	StringStream ss(text);
+	int pos = 0;
+	int begin = text.Find("3  Malformed sequences");
+	int end   = text.Find("5.3 Noncharacter code positions");
+	ASSERT(begin >= 0 && begin < end);
+	while(!ss.IsEof()) {
+		String line = ss.GetLine();
+		ValidateUtf8(line, begin, end, pos++);
+	}
+}
diff --git a/autotest/StreamUTF8Test/StreamUTF8Test.upp b/autotest/StreamUTF8Test/StreamUTF8Test.upp
new file mode 100644
index 000000000..ec803701a
--- /dev/null
+++ b/autotest/StreamUTF8Test/StreamUTF8Test.upp
@@ -0,0 +1,11 @@
+description "Check's Stream's Utf8 decoder for incomplete, invalid and overlong sequences\377";
+
+uses
+	Core;
+
+file
+	StreamUTF8Test.cpp;
+
+mainconfig
+	"" = "";
+
diff --git a/autotest/StreamUTF8Test/utf8_stress_test.txt b/autotest/StreamUTF8Test/utf8_stress_test.txt
new file mode 100644
index 000000000..a5b5d50e6
Binary files /dev/null and b/autotest/StreamUTF8Test/utf8_stress_test.txt differ
diff --git a/uppsrc/Core/Stream.cpp b/uppsrc/Core/Stream.cpp
index 53c8642e7..51f0274bf 100644
--- a/uppsrc/Core/Stream.cpp
+++ b/uppsrc/Core/Stream.cpp
@@ -224,76 +224,58 @@ int64  Stream::_Get64() {
 int Stream::GetUtf8()
 {
 	int code = Get();
+	
 	if(code <= 0) {
 		LoadError();
 		return -1;
 	}
+
 	if(code < 0x80)
 		return code;
-	else
-	if(code < 0xC2)
-		return -1;
-	else
-	if(code < 0xE0) {
-		if(IsEof()) {
-			LoadError();
-			return -1;
+	
+	if(code >= 0xC2) {
+		int c = 0, pos = GetPos();
+		if(code < 0xE0) {
+			int c0 = Get();
+			if(c0 >= 0x80 && c0 < 0xC0 &&
+			   (c = ((code - 0xC0) << 6) + c0 - 0x80) >= 0x80 && c < 0x800) {
+					return c;
+			}
+			if(c0 < 0)
+				LoadError();
 		}
-		return ((code - 0xC0) << 6) + Get() - 0x80;
+		else
+		if(code < 0xF0) {
+			int c0 = Get();
+			int c1 = Get();
+			if(c1 >= 0x80 && c1 < 0xC0 &&
+			   c0 >= 0x80 && c0 < 0xC0 &&
+			   (c = ((code - 0xE0) << 12) + ((c0 - 0x80) << 6) + c1 - 0x80) >= 0x800 && c < 0x10000) {
+					return c;
+			}
+			if(c1 < 0)
+				LoadError();
+			   
+		}
+		else
+		if(code < 0xF8) {
+			int c0 = Get();
+			int c1 = Get();
+			int c2 = Get();
+			if(c2 >= 0x80 && c2 < 0xC0 &&
+			   c1 >= 0x80 && c1 < 0xC0 &&
+			   c0 >= 0x80 && c0 < 0xC0 &&
+			   (c = ((code - 0xF0) << 18) + ((c0 - 0x80) << 12) + ((c1 - 0x80) << 6) + c2 - 0x80) >= 0x10000 && c < 0x110000) {
+					return c;
+			}
+			if(c2 < 0)
+				LoadError();
+		}
+		if(!IsError())
+			Seek(pos); // Rewind (to represent each invalid byte).
 	}
-	else
-	if(code < 0xF0) {
-		int c0 = Get();
-		int c1 = Get();
-		if(c1 < 0) {
-			LoadError();
-			return -1;
-		}
-		return ((code - 0xE0) << 12) + ((c0 - 0x80) << 6) + c1 - 0x80;
-	}
-	else
-	if(code < 0xF8) {
-		int c0 = Get();
-		int c1 = Get();
-		int c2 = Get();
-		if(c2 < 0) {
-			LoadError();
-			return -1;
-		}
-		return ((code - 0xf0) << 18) + ((c0 - 0x80) << 12) + ((c1 - 0x80) << 6) + c2 - 0x80;
-	}
-	else
-	if(code < 0xFC) {
-		int c0 = Get();
-		int c1 = Get();
-		int c2 = Get();
-		int c3 = Get();
-		if(c3 < 0) {
-			LoadError();
-			return -1;
-		}
-		return ((code - 0xF8) << 24) + ((c0 - 0x80) << 18) + ((c1 - 0x80) << 12) +
-		       ((c2 - 0x80) << 6) + c3 - 0x80;
-	}
-	else
-	if(code < 0xFE) {
-		int c0 = Get();
-		int c1 = Get();
-		int c2 = Get();
-		int c3 = Get();
-		int c4 = Get();
-		if(c4 < 0) {
-			LoadError();
-			return -1;
-		}
-		return ((code - 0xFC) << 30) + ((c0 - 0x80) << 24) + ((c1 - 0x80) << 18) +
-		       ((c2 - 0x80) << 12) + ((c3 - 0x80) << 6) + c4 - 0x80;
 
-	}
-	else {
-		LoadError();
-		return -1;
-	}
+	return -1;
 }
 
 String Stream::GetLine() {