diff --git a/src/text_file_reader.cpp b/src/text_file_reader.cpp
index 317b44e36e..6e6b14a519 100644
--- a/src/text_file_reader.cpp
+++ b/src/text_file_reader.cpp
@@ -42,8 +42,9 @@ using namespace LAMMPS_NS;
  * \param  filetype  Description of file type for error messages */
 
 TextFileReader::TextFileReader(const std::string &filename, const std::string &filetype) :
-    filetype(filetype), closefp(true), ignore_comments(true)
+    filetype(filetype), closefp(true), line(nullptr), ignore_comments(true)
 {
+  set_bufsize(1024);
   fp = fopen(filename.c_str(), "r");
 
   if (fp == nullptr) {
@@ -70,8 +71,9 @@ This function is useful in combination with :cpp:func:`utils::open_potential`.
  * \param  filetype  Description of file type for error messages */
 
 TextFileReader::TextFileReader(FILE *fp, std::string filetype) :
-    filetype(std::move(filetype)), closefp(false), fp(fp), ignore_comments(true)
+    filetype(std::move(filetype)), closefp(false), line(nullptr), fp(fp), ignore_comments(true)
 {
+  set_bufsize(1024);
   if (fp == nullptr) throw FileReaderException("Invalid file descriptor");
 }
 
@@ -80,6 +82,20 @@ TextFileReader::TextFileReader(FILE *fp, std::string filetype) :
 TextFileReader::~TextFileReader()
 {
   if (closefp) fclose(fp);
+  delete[] line;
+}
+
+/** adjust line buffer size */
+
+void TextFileReader::set_bufsize(int newsize)
+{
+  if (newsize < 100) {
+    throw FileReaderException(
+        fmt::format("line buffer size {} for {} file too small, must be > 100", newsize, filetype));
+  }
+  delete[] line;
+  bufsize = newsize;
+  line = new char[bufsize];
 }
 
 /** Reset file to the beginning */
@@ -93,7 +109,7 @@ void TextFileReader::rewind()
 
 void TextFileReader::skip_line()
 {
-  char *ptr = fgets(line, MAXLINE, fp);
+  char *ptr = fgets(line, bufsize, fp);
   if (ptr == nullptr) {
     // EOF
     throw EOFException(fmt::format("Missing line in {} file!", filetype));
@@ -120,7 +136,7 @@ char *TextFileReader::next_line(int nparams)
   int n = 0;
   int nwords = 0;
 
-  char *ptr = fgets(line, MAXLINE, fp);
+  char *ptr = fgets(line, bufsize, fp);
 
   if (ptr == nullptr) {
     // EOF
@@ -134,7 +150,7 @@ char *TextFileReader::next_line(int nparams)
   if (nwords > 0) n = strlen(line);
 
   while (nwords == 0 || nwords < nparams) {
-    ptr = fgets(&line[n], MAXLINE - n, fp);
+    ptr = fgets(&line[n], bufsize - n, fp);
 
     if (ptr == nullptr) {
       // EOF
diff --git a/src/text_file_reader.h b/src/text_file_reader.h
index 30ec9351be..017a721e67 100644
--- a/src/text_file_reader.h
+++ b/src/text_file_reader.h
@@ -26,8 +26,8 @@ namespace LAMMPS_NS {
 class TextFileReader {
   std::string filetype;
   bool closefp;
-  static constexpr int MAXLINE = 1024;
-  char line[MAXLINE];
+  int bufsize;
+  char *line;
   FILE *fp;
 
  public:
@@ -35,9 +35,13 @@ class TextFileReader {
 
   TextFileReader(const std::string &filename, const std::string &filetype);
   TextFileReader(FILE *fp, std::string filetype);
+  TextFileReader() = delete;
+  TextFileReader(const TextFileReader &) = delete;
+  TextFileReader(const TextFileReader &&) = delete;
+  TextFileReader &operator=(const TextFileReader &) = delete;
+  virtual ~TextFileReader();
 
-  ~TextFileReader();
-
+  void set_bufsize(int);
   void rewind();
   void skip_line();
   char *next_line(int nparams = 0);