diff --git a/extendr-api/src/lib.rs b/extendr-api/src/lib.rs
index 04f99650b1..eef61eb622 100644
--- a/extendr-api/src/lib.rs
+++ b/extendr-api/src/lib.rs
@@ -418,8 +418,10 @@ pub const NA_STRING: Option<&str> = None;
 pub const NA_LOGICAL: Rbool = Rbool::na_value();
 
 thread_local! {
-    pub static R_FACTOR_STRING: once_cell::unsync::Lazy<Robj> = once_cell::unsync::Lazy::new(||{
-        "factor".into_robj()
+    #[allow(non_upper_case_globals)]
+    pub static R_FactorSymbol: once_cell::unsync::Lazy<SEXP> = once_cell::unsync::Lazy::new(||{
+        let factor_c_string = CString::new("factor").unwrap();
+        unsafe { libR_sys::Rf_install(factor_c_string.as_ptr()) }
     });
 }
 
diff --git a/extendr-macros/src/extendr_enum.rs b/extendr-macros/src/extendr_enum.rs
index 6d2a4e5d21..caab64422b 100644
--- a/extendr-macros/src/extendr_enum.rs
+++ b/extendr-macros/src/extendr_enum.rs
@@ -110,9 +110,12 @@ pub(crate) fn extendr_enum(item_enum: syn::ItemEnum) -> proc_macro::TokenStream
                         let strings_enum = once_cell::unsync::Lazy::force(strings_enum);
                         libR_sys::Rf_setAttrib(robj.get(), libR_sys::R_LevelsSymbol, strings_enum.get());
                     });
-                    extendr_api::R_FACTOR_STRING.with(|factor_class| {
+                    extendr_api::R_FactorSymbol.with(|factor_class| {
                         let factor_class = once_cell::unsync::Lazy::force(factor_class);
-                        libR_sys::Rf_setAttrib(robj.get(), libR_sys::R_ClassSymbol, factor_class.get());
+                        // a symbol is permanent, so no need to protect it
+                        // printname is CHARSXP, and we need a STRSXP, hence `Rf_ScalarString`
+                        // doesn't need protection, because it gets inserted into a protected `SEXP` immediately
+                        libR_sys::Rf_setAttrib(robj.get(), libR_sys::R_ClassSymbol, libR_sys::Rf_ScalarString(libR_sys::PRINTNAME(*factor_class)));
                     });
                 }
                 Ok(robj)