diff --git a/doc/src/Errors_messages.rst b/doc/src/Errors_messages.rst
index 4866de31c6..d4aca3f9aa 100644
--- a/doc/src/Errors_messages.rst
+++ b/doc/src/Errors_messages.rst
@@ -4729,6 +4729,12 @@ Doc page with :doc:`WARNING messages <Errors_warnings>`
 *Invalid Masses section in molecule file*
    Self-explanatory.
 
+*Invalid molecule ID in molecule file*
+   Molecule ID must be a non-zero positive integer.
+
+*Invalid Molecules section in molecule file*   
+   Self-explanatory.
+
 *Invalid REAX atom type*
    There is a mis-match between LAMMPS atom types and the elements
    listed in the ReaxFF force field file.
diff --git a/src/molecule.h b/src/molecule.h
index bc696dab74..fac5202d9f 100644
--- a/src/molecule.h
+++ b/src/molecule.h
@@ -365,6 +365,14 @@ E: Invalid improper type in impropers section of molecule file
 
 Self-explanatory.
 
+E: Invalid molecule ID in molecule file
+
+Molecule ID must be a non-zero positive integer.
+
+E: Invalid Molecules section in molecule file
+
+Self-explanatory.
+
 E: Invalid Special Bond Counts section in molecule file
 
 Self-explanatory.