diff --git a/stfpy/stfpy/stf_inst_reader.pxd b/stfpy/stfpy/stf_inst_reader.pxd
index 9790186..3531d71 100644
--- a/stfpy/stfpy/stf_inst_reader.pxd
+++ b/stfpy/stfpy/stf_inst_reader.pxd
@@ -13,8 +13,8 @@ cdef class HeaderCommentsTypeIterator:
     @staticmethod
     cdef inline HeaderCommentsTypeIterator _construct(const _HeaderCommentsType* vec):
         it = HeaderCommentsTypeIterator()
-        it.c_it = dereference(vec).begin()
-        it.c_end_it = dereference(vec).end()
+        it.c_it = dereference(vec).const_begin()
+        it.c_end_it = dereference(vec).const_end()
         return it
 
 cdef class HeaderCommentsType:
diff --git a/stfpy/stfpy/stf_lib/stf_inst_reader.pxd b/stfpy/stfpy/stf_lib/stf_inst_reader.pxd
index dcd7176..3ea56bc 100644
--- a/stfpy/stfpy/stf_lib/stf_inst_reader.pxd
+++ b/stfpy/stfpy/stf_lib/stf_inst_reader.pxd
@@ -2,7 +2,7 @@
 
 from libc.stdint cimport *
 from libcpp.vector cimport vector
-from cython.cimports.libcpp.string import string
+from libcpp.string cimport string
 from stfpy.stf_lib.stf_inst cimport STFInst
 
 ctypedef vector[string] HeaderCommentsType