diff --git a/src/column.cpp b/src/column.cpp
index 1729f42..3f43a9e 100644
--- a/src/column.cpp
+++ b/src/column.cpp
@@ -171,7 +171,7 @@ RObject columnsToDf(std::vector<ColumnPtr> columns, Rcpp::CharacterVector names,
     if (columns[i]->has_failures()) {
       std::string message = columns[i]->describe_failures(
               Rcpp::as<std::string>(names[static_cast<long>(i)]));
-      Rf_warning(message.c_str());
+      Rf_warning("%s", message.c_str());
     }
     out[static_cast<long>(i)] = columns[i]->vector();
   }
diff --git a/tests/testthat/test-coltype-warning.R b/tests/testthat/test-coltype-warning.R
new file mode 100644
index 0000000..3e6d85a
--- /dev/null
+++ b/tests/testthat/test-coltype-warning.R
@@ -0,0 +1,26 @@
+test_that("bad column types generates warning", {
+  expect_warning(
+    hipread_long(
+      hipread_example("test-basic.dat"),
+      list(
+        H = hip_fwf_widths(
+          c(1, 3, 3, 3, 2),
+          c("rt", "hhnum", "hh_char", "hh_dbl", "hh_impdbl"),
+          # Misspecify hh_char as a double type
+          c("character", "character", "double", "double", "double"),
+          trim_ws = c(TRUE, FALSE, TRUE, NA, NA),
+          imp_dec = c(NA, NA, NA, 0, 1)
+        ),
+        P = hip_fwf_widths(
+          c(1, 3, 1, 3, 1),
+          c("rt", "hhnum", "pernum", "per_dbl", "per_mix"),
+          c("character", "character", "integer", "double", "character"),
+          trim_ws = c(TRUE, FALSE, NA, NA, TRUE),
+          imp_dec = c(NA, NA, NA, 0, NA)
+        )
+      ),
+      hip_rt(1, 1)
+    ),
+    regexp = "could not convert"
+  )
+})