diff --git a/README b/README
new file mode 100644
index 0000000..3bb672f
--- /dev/null
+++ b/README
@@ -0,0 +1,3 @@
+This project is a forked version of pyQuant as modified on November 01, 2017.
+
+Key customization include accommodating the custom modifications under valid assumptions.
diff --git a/pyquant/worker.py b/pyquant/worker.py
index 2307b81..24cbe68 100644
--- a/pyquant/worker.py
+++ b/pyquant/worker.py
@@ -4,7 +4,7 @@
 import copy
 import operator
 import traceback
-
+import re
 from functools import cmp_to_key
 
 import pandas as pd
@@ -341,22 +341,29 @@ def quantify_peaks(self, params):
                 else:
                     if peptide:
                         for label_mass, label_masses in silac_masses.items():
+                            added_residues = added_residues.union(label_masses)
+#                            labels = [label_mass for mod_aa in peptide if mod_aa in label_masses]
+# Replaced above line to look for terminal amino acid modifications status mass difference
+                            labels = 0
+                            for mod_aa in peptide:
+                                if mod_aa in label_masses:
+                                    labels += label_mass
+                            for l_masses in label_masses:
+                                if len(l_masses) > 1 and re.search(l_masses, peptide):
+                                    labels += label_mass
                             if 'X' in label_masses:
                                 global_mass = label_mass
                             if ']' in label_masses:
                                 cterm_mass = label_mass
                             if '[' in label_masses:
                                 nterm_mass = label_mass
-                            added_residues = added_residues.union(label_masses)
-                            labels = [label_mass for mod_aa in peptide if mod_aa in label_masses]
-                            silac_shift += sum(labels)
+                            silac_shift += labels
                     else:
                         # no mass, just assume we have one of the labels
                         silac_shift += mass_keys[0]
                     if global_mass is not None:
                         silac_shift += sum([global_mass for mod_aa in peptide if mod_aa not in added_residues])
                     silac_shift += cterm_mass + nterm_mass
-
                     label_mz = precursor + (silac_shift / float(charge))
                     theo_mz = theor_mass + (silac_shift / float(charge))
                 precursors[silac_label]['uncalibrated_mz'] = label_mz