diff --git a/src/freadR.c b/src/freadR.c
index 777a8bbf13..9338dbf61a 100644
--- a/src/freadR.c
+++ b/src/freadR.c
@@ -832,8 +832,8 @@ SEXP spillConnectionToFile(SEXP connection, SEXP tempfile_path, SEXP nrows_limit
 
   const double nrows_max = REAL_RO(nrows_limit)[0];
   if (R_FINITE(nrows_max) && nrows_max >= 0.0) {
-    if (nrows_max > SIZE_MAX)
-      STOP(_("spillConnectionToFile: nrows_limit (%g) must fit into a native-size unsigned integer (<= %zu)"), nrows_max, (size_t)SIZE_MAX); // # nocov
+    if (nrows_max >= (double)SIZE_MAX)
+      STOP(_("spillConnectionToFile: nrows_limit (%g) must fit into a native-size unsigned integer (< %zu)"), nrows_max, (size_t)SIZE_MAX); // # nocov
     state.row_limit = (size_t)nrows_max;
     if (state.row_limit == 0) state.row_limit = 100;  // read at least 100 rows if nrows==0
     state.row_limit++; // cater for potential header row
diff --git a/src/nafill.c b/src/nafill.c
index 43146f9dc8..8a8e8eab56 100644
--- a/src/nafill.c
+++ b/src/nafill.c
@@ -247,6 +247,7 @@ SEXP nafillR(SEXP obj, SEXP type, SEXP fill, SEXP nan_is_na_arg, SEXP inplace, S
     }
   }
   // need any_char guard to avoid parallelizing on character columns
+  (void)any_char; // used only by OpenMP-enabled builds; avoid -Wunused-but-set-variable otherwise
   #pragma omp parallel for if (nx>1 && !any_char) num_threads(getDTthreads(nx, true))
   for (R_len_t i=0; i<nx; i++) {
     switch (TYPEOF(VECTOR_ELT(x, i))) {