diff --git a/doc/src/Errors_messages.rst b/doc/src/Errors_messages.rst
index 6bf2e1092c..f2c57a0286 100644
--- a/doc/src/Errors_messages.rst
+++ b/doc/src/Errors_messages.rst
@@ -5708,6 +5708,9 @@ Doc page with :doc:`WARNING messages <Errors_warnings>`
 *Molecule file has dihedrals but no ndihedrals setting*
    Self-explanatory.
 
+*Molecule file has fragments but no nfragments setting*
+   Self-explanatory.
+
 *Molecule file has impropers but no nimpropers setting*
    Self-explanatory.
 
@@ -5717,6 +5720,12 @@ Doc page with :doc:`WARNING messages <Errors_warnings>`
 *Molecule file has no Body Integers section*
    Self-explanatory.
 
+*Molecule file has no Fragments section*
+   Self-explanatory.
+
+*Molecule file has no Molecules section*
+   Self-explanatory.
+
 *Molecule file has special flags but no bonds*
    Self-explanatory.
 
diff --git a/src/molecule.h b/src/molecule.h
index 5a3fa5a327..d7ada5b813 100644
--- a/src/molecule.h
+++ b/src/molecule.h
@@ -241,6 +241,10 @@ E: Molecule file has impropers but no nimpropers setting
 
 Self-explanatory.
 
+E: Molecule file has fragments but no nfragments setting
+
+Self-explanatory.
+
 E: Molecule file shake flags not before shake atoms
 
 The order of the two sections is important.
@@ -277,6 +281,14 @@ E: Molecule file has no Body Doubles section
 
 Self-explanatory.
 
+E: Molecule file has no Molecules section
+
+Self-explanatory.
+
+E: Molecule file has no Fragments section
+
+Self-explanatory.
+
 E: Cannot auto-generate special bonds before simulation box is defined
 
 UNDOCUMENTED