diff --git a/src/fwrite.c b/src/fwrite.c
index 986d27908..d587329d6 100644
--- a/src/fwrite.c
+++ b/src/fwrite.c
@@ -166,7 +166,8 @@ SEXP writefile(SEXP list_of_columns,
       error("Column %d's length (%d) is not the same as column 1's length (%d)", i+1, length(VECTOR_ELT(list_of_columns, i)), nrows);
   }
 #ifndef _OPENMP
-  warning("Your platform/environment has not detected OpenMP support. fwrite() will still work, but slower in single threaded mode.");
+  Rprintf("Your platform/environment has not detected OpenMP support. fwrite() will still work, but slower in single threaded mode.\n");
+  // Rprintf rather than warning() because warning() would cause test.data.table() to error about the unexpected warnings
 #endif 
   const Rboolean verbose = LOGICAL(verboseArg)[0];
   const Rboolean quote = LOGICAL(quoteArg)[0];