diff --git a/src/errors.cpp b/src/errors.cpp
index bfcbd2f..2dd9bf7 100644
--- a/src/errors.cpp
+++ b/src/errors.cpp
@@ -34,6 +34,7 @@ const std::array<const char *, (std::size_t)ErrorCode::NumErrors> error_texts{
 "Array has zero length.",
 "Could not open file.",
 "Writing to file failed.",
+"Required argument is NULL.",
 };
 
 // clang-format on
diff --git a/src/errors.hpp b/src/errors.hpp
index abf0af1..ee75787 100644
--- a/src/errors.hpp
+++ b/src/errors.hpp
@@ -35,6 +35,7 @@ enum class ErrorCode : int32_t {
     ZeroLengthArray,
     CouldNotOpenFile,
     FileWriteError,
+    ArgIsNull,
     // When you add an error code here, also add the string representation in the .cpp file.
     NumErrors,
 };
diff --git a/src/pdfcapi.cpp b/src/pdfcapi.cpp
index 83eecde..9d64320 100644
--- a/src/pdfcapi.cpp
+++ b/src/pdfcapi.cpp
@@ -21,6 +21,11 @@
 
 using namespace A4PDF;
 
+#define CHECK_NULL(x)                                                                              \
+    if(x == nullptr) {                                                                             \
+        return (A4PDF_EC)ErrorCode::ArgIsNull;                                                     \
+    }
+
 A4PDF_EC a4pdf_options_new(A4PDF_Options **out_ptr) A4PDF_NOEXCEPT {
     *out_ptr = reinterpret_cast<A4PDF_Options *>(new PdfGenerationData());
     return (A4PDF_EC)ErrorCode::NoError;
@@ -49,6 +54,9 @@ A4PDF_PUBLIC A4PDF_EC a4pdf_options_set_mediabox(
 A4PDF_EC a4pdf_generator_new(const char *filename,
                              const A4PDF_Options *options,
                              A4PDF_Generator **out_ptr) A4PDF_NOEXCEPT {
+    CHECK_NULL(filename);
+    CHECK_NULL(options);
+    CHECK_NULL(out_ptr);
     auto opts = reinterpret_cast<const PdfGenerationData *>(options);
     *out_ptr = reinterpret_cast<A4PDF_Generator *>(new PdfGen(filename, *opts));
     return (A4PDF_EC)ErrorCode::NoError;