diff --git a/src/check_mmCIF.jl b/src/check_mmCIF.jl
index 40cc93c..e0935b0 100644
--- a/src/check_mmCIF.jl
+++ b/src/check_mmCIF.jl
@@ -89,6 +89,7 @@ function _check_mmCIF(data::Union{IOStream, IOBuffer})
             end
         end
     end
+    seekstart(data)
     if mmCIF
         if mmCIF_fields.name == 0 ||
            mmCIF_fields.resname == 0 ||
diff --git a/src/readPDB.jl b/src/readPDB.jl
index 50f7a2b..394fef7 100644
--- a/src/readPDB.jl
+++ b/src/readPDB.jl
@@ -103,6 +103,7 @@ function _parse_pdb(
             lastatom = atom
         end
     end
+    seekstart(pdbdata)
     if natoms == 0
         error(" Could not find any atom in PDB file matching the selection. ")
     end