diff --git a/Sming/Core/Data/Stream/IFS/FileStream.cpp b/Sming/Core/Data/Stream/IFS/FileStream.cpp
index a046ad3ef3..9cdf0eb02c 100644
--- a/Sming/Core/Data/Stream/IFS/FileStream.cpp
+++ b/Sming/Core/Data/Stream/IFS/FileStream.cpp
@@ -10,8 +10,6 @@
 
 #include "FileStream.h"
 
-#define ETAG_SIZE 16
-
 namespace IFS
 {
 void FileStream::attach(FileHandle file, size_t size)
@@ -172,10 +170,27 @@ String FileStream::id() const
 		return nullptr;
 	}
 
-	char buf[ETAG_SIZE];
-	m_snprintf(buf, ETAG_SIZE, _F("00f-%x-%x0-%x"), stat.id, stat.size, stat.name.length);
-
-	return String(buf);
+	/*
+		Jan 2024. How ETAGs are generated is not specified. Previous implementation was like this:
+
+			m_snprintf(buf, ETAG_SIZE, _F("00f-%x-%x0-%x"), stat.id, stat.size, stat.name.length);
+
+		Issues are:
+			- on some architectures compiler warns about differing types %x vs arguments
+			- name can change without length being affected; if name changes then file lookup would fail anyway
+			- modification timestamp is a good metric, should be incorporated
+	*/
+	String id;
+	id += "00f-";
+	id += String(stat.id, HEX);
+	id += '-';
+	id += String(stat.size, HEX);
+	id += '-';
+	id += String(stat.mtime, HEX);
+	id += '-';
+	id += String(stat.name.length, HEX);
+
+	return id;
 }
 
 bool FileStream::truncate(size_t newSize)
diff --git a/tests/HostTests/modules/Files.cpp b/tests/HostTests/modules/Files.cpp
index 05eef51a4b..ed25524c7f 100644
--- a/tests/HostTests/modules/Files.cpp
+++ b/tests/HostTests/modules/Files.cpp
@@ -88,6 +88,7 @@ class FilesTest : public TestGroup
 		{
 			fileSetContent(testFileName, testContent);
 			FileStream fs(testFileName);
+			Serial << testFileName << " ID: " << fs.id() << endl;
 			res = fs.truncate(100);
 			pos = fs.getPos();
 			size = fs.getSize();