diff --git a/module/language/cps/effects-analysis.scm b/module/language/cps/effects-analysis.scm
index 4ca6e9815..3c2b5da54 100644
--- a/module/language/cps/effects-analysis.scm
+++ b/module/language/cps/effects-analysis.scm
@@ -364,6 +364,8 @@
 
 ;; Bytevectors.
 (define-primitive-effects
+  ((bytevector-length _) (cause &type-check))
+
   ((bv-u8-ref bv n) (logior (cause &type-check) &bytevector))
   ((bv-s8-ref bv n) (logior (cause &type-check) &bytevector))
   ((bv-u16-ref bv n) (logior (cause &type-check) &bytevector))
diff --git a/module/language/tree-il/primitives.scm b/module/language/tree-il/primitives.scm
index 170338425..a959df25d 100644
--- a/module/language/tree-il/primitives.scm
+++ b/module/language/tree-il/primitives.scm
@@ -94,6 +94,8 @@
 
     allocate-struct struct-vtable make-struct struct-ref struct-set!
 
+    bytevector-length
+
     bytevector-u8-ref bytevector-u8-set!
     bytevector-s8-ref bytevector-s8-set!
     u8vector-ref u8vector-set! s8vector-ref s8vector-set!
@@ -172,7 +174,7 @@
     char<? char<=? char>=? char>?
     integer->char char->integer number->string string->number
     struct-vtable
-    length string-length vector-length
+    length string-length vector-length bytevector-length
     ;; These all should get expanded out by expand-primitives.
     caar cadr cdar cddr
     caaar caadr cadar caddr cdaar cdadr cddar cdddr