diff --git a/src/serialization.jl b/src/serialization.jl
index 395940c7..26ce9837 100644
--- a/src/serialization.jl
+++ b/src/serialization.jl
@@ -2,7 +2,7 @@ function Serialization.serialize(s::AbstractSerializer, A::GBVecOrMat)
     Serialization.writetag(s.io, Serialization.OBJECT_TAG)
     Serialization.serialize(s, typeof(A))
     v = Vector{UInt8}(undef, serialize_sizehint(A))
-    sz = Ref{LibGraphBLAS.GrB_Index}()
+    sz = Ref{LibGraphBLAS.GrB_Index}(length(v))
     @wraperror LibGraphBLAS.GrB_Matrix_serialize(v, sz, A)
     resize!(v, sz[])
     serialize(s, v)