diff --git a/src/attributes.jl b/src/attributes.jl
index 0c683224..9af867dd 100644
--- a/src/attributes.jl
+++ b/src/attributes.jl
@@ -173,8 +173,13 @@ end
 function write_attribute(attr::Attribute, memtype::Datatype, str::AbstractString)
     strbuf = Base.cconvert(Cstring, str)
     GC.@preserve strbuf begin
-        buf = Base.unsafe_convert(Ptr{UInt8}, strbuf)
-        write_attribute(attr, memtype, buf)
+        if API.h5t_is_variable_str(memtype)
+            ptr = Base.unsafe_convert(Cstring, strbuf)
+            write_attribute(attr, memtype, Ref(ptr))
+        else
+            ptr = Base.unsafe_convert(Ptr{UInt8}, strbuf)
+            write_attribute(attr, memtype, ptr)
+        end
     end
 end
 function write_attribute(
diff --git a/test/attributes.jl b/test/attributes.jl
index b2a71028..4d7111b2 100644
--- a/test/attributes.jl
+++ b/test/attributes.jl
@@ -69,3 +69,13 @@ end
         close(f)
     end
 end
+
+@testset "variable length strings" begin
+    filename = tempname()
+    h5open(filename, "w") do f
+        # https://github.com/JuliaIO/HDF5.jl/issues/1129
+        attr = create_attribute(f, "attr-name", datatype(String), dataspace(String))
+        write_attribute(attr, datatype(String), "attr-value")
+        @test attrs(f)["attr-name"] == "attr-value"
+    end
+end