diff --git a/README.md b/README.md
index 79c690b..3828a0c 100644
--- a/README.md
+++ b/README.md
@@ -52,8 +52,14 @@ All features of upskirt are supported, including:
     errors that were present in the C code).
 
 *   Good performance. I have not done rigorous benchmarking, but
-    informal testing suggests it is pretty fast. Probably not as
-    fast as upskirt, but probably faster than most others.
+    informal testing suggests it is around 8x slower than upskirt.
+    This is still an ugly, direct translation from the C code, so
+    the difference is unlikely to be related to differences in
+    coding style. There is a lot of bounds checking that is
+    duplicated (by user code for the application and again by code
+    the compiler generates) and there is some additional memory
+    management overhead, since I allocate and garbage collect
+    buffers instead of explicitly managing them as upskirt does.
 
 *   Minimal dependencies. blackfriday only depends on standard
     library packages in Go. The source code is pretty