diff --git a/src/lib.rs b/src/lib.rs
index 46d13f5..4fd1c29 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -31,6 +31,10 @@ impl<const N: usize> ReadWriteBuf<N> {
         self.read_cursor == self.write_cursor && !self.full
     }
 
+    pub fn is_full(&self) -> bool {
+        self.full
+    }
+
     pub fn for_reading(&mut self) -> Option<&mut [u8]> {
         let (start, stop) = if self.read_cursor < self.write_cursor {
             (self.read_cursor, self.write_cursor)
@@ -64,7 +68,7 @@ impl<const N: usize> ReadWriteBuf<N> {
 
     pub fn advance_write(&mut self, count: usize) {
         self.write_cursor = (self.write_cursor + count) % N;
-        if self.write_cursor != self.read_cursor {
+        if count > 0 {
             self.full = false;
         }
     }
@@ -74,6 +78,32 @@ impl<const N: usize> ReadWriteBuf<N> {
 mod tests {
     use super::ReadWriteBuf;
 
+    #[test]
+    fn read_exact_length_works() {
+        let mut buf = ReadWriteBuf::<10>::new();
+        assert!(buf.is_empty());
+        assert!(buf.for_writing().is_none());
+
+        let read_into = buf.for_reading().unwrap();
+        assert_eq!(read_into.len(), 10);
+        buf.advance_read(10);
+
+        assert!(buf.is_full());
+        assert_eq!(buf.read_cursor, buf.write_cursor);
+
+        let write_from = buf.for_writing().unwrap();
+        assert_eq!(write_from.len(), 10);
+        buf.advance_write(10);
+
+        assert!(!buf.full);
+        assert_eq!(buf.read_cursor, buf.write_cursor);
+
+        let read_from = buf.for_reading().unwrap();
+        assert_eq!(read_from.len(), 10);
+
+        assert!(buf.for_writing().is_none());
+    }
+
     #[test]
     fn from_0_0_reads_whole_len() {
         let mut buf = ReadWriteBuf::<16>::new();