diff --git a/src/system/libroot/posix/fcntl.cpp b/src/system/libroot/posix/fcntl.cpp
index ad9874a3f1..0bfa7f9977 100644
--- a/src/system/libroot/posix/fcntl.cpp
+++ b/src/system/libroot/posix/fcntl.cpp
@@ -102,5 +102,13 @@ posix_fallocate(int fd, off_t offset, off_t len)
 	if (len == 0 || offset < 0)
 		return EINVAL;
 
-	return _kern_preallocate(fd, offset, len);
+	int error = _kern_preallocate(fd, offset, len);
+	if (error == B_UNSUPPORTED) {
+		// While the official specification for this function does not
+		// prescribe which error code to use when the underlying file system
+		// does not support preallocation, we will convert B_UNSUPPORTED to
+		// EOPNOTSUPP for better compatibility with existing applications.
+		return EOPNOTSUPP;
+	}
+	return error;
 }