diff --git a/mzLib/MzLibUtil/MzLibException.cs b/mzLib/MzLibUtil/MzLibException.cs
index 61ecc8d6b..885081433 100644
--- a/mzLib/MzLibUtil/MzLibException.cs
+++ b/mzLib/MzLibUtil/MzLibException.cs
@@ -1,8 +1,9 @@
-using System;
+#nullable enable
+using System;
 
 namespace MzLibUtil
 {
     [Serializable]
-    public class MzLibException(string message, Exception innerException = null) 
+    public class MzLibException(string message, Exception? innerException = null) 
         : Exception(message, innerException);
 }
\ No newline at end of file
diff --git a/mzLib/Omics/IBioPolymerWithSetMods.cs b/mzLib/Omics/IBioPolymerWithSetMods.cs
index 0b9926a01..12989b1f3 100644
--- a/mzLib/Omics/IBioPolymerWithSetMods.cs
+++ b/mzLib/Omics/IBioPolymerWithSetMods.cs
@@ -82,5 +82,86 @@ public static string GetBaseSequenceFromFullSequence(string fullSequence)
             }
             return sb.ToString();
         }
+
+        /// <summary>
+        /// Returns a list of modifications and their OneBased index from a full sequence
+        /// </summary>
+        /// <param name="fullSequence">Full sequence</param>
+        /// <param name="allModsKnown">All known modifications</param>
+        /// <returns></returns>
+        /// <exception cref="MzLibUtil.MzLibException">When a full sequence is not in the correct format or a mod is not found in the allModsKnown dictionary</exception>
+        public static Dictionary<int, Modification> GetModificationDictionaryFromFullSequence(string fullSequence,
+            Dictionary<string, Modification> allModsKnown)
+        {
+            var allModsOneIsNterminus = new Dictionary<int, Modification>();
+            var baseSequence = GetBaseSequenceFromFullSequence(fullSequence);
+            int currentModStart = 0;
+            int currentModificationLocation = 1;
+            bool currentlyReadingMod = false;
+            int bracketCount = 0;
+
+            for (int r = 0; r < fullSequence.Length; r++)
+            {
+                char c = fullSequence[r];
+                if (c == '[')
+                {
+                    currentlyReadingMod = true;
+                    if (bracketCount == 0)
+                    {
+                        currentModStart = r + 1;
+                    }
+                    bracketCount++;
+                }
+                else if (c == ']')
+                {
+                    string modId = null;
+                    bracketCount--;
+                    if (bracketCount == 0)
+                    {
+                        try
+                        {
+                            //remove the beginning section (e.g. "Fixed", "Variable", "Uniprot")
+                            string modString = fullSequence.Substring(currentModStart, r - currentModStart);
+                            int splitIndex = modString.IndexOf(':');
+                            string modType = modString.Substring(0, splitIndex);
+                            modId = modString.Substring(splitIndex + 1, modString.Length - splitIndex - 1);
+                        }
+                        catch (Exception e)
+                        {
+                            throw new MzLibUtil.MzLibException(
+                                "Error while trying to parse string into peptide: " + e.Message, e);
+
+                        }
+                        if (!allModsKnown.TryGetValue(modId, out var mod))
+                        {
+                            throw new MzLibUtil.MzLibException(
+                                "Could not find modification while reading string: " + fullSequence);
+                        }
+                        if (mod.LocationRestriction.Contains("C-terminal.") && r == fullSequence.Length - 1)
+                        {
+                            currentModificationLocation = baseSequence.Length + 2;
+                        }
+                        allModsOneIsNterminus.Add(currentModificationLocation, mod);
+                        currentlyReadingMod = false;
+                    }
+                }
+                else if (!currentlyReadingMod)
+                {
+                    currentModificationLocation++;
+                }
+                //else do nothing
+            }
+
+            return allModsOneIsNterminus;
+        }
+
+        /// <summary>
+        /// Returns a list of modifications from a full sequence
+        /// </summary>
+        /// <param name="fullSequence">Full sequence</param>
+        /// <param name="allModsKnown">All known modifications</param>
+        /// <returns></returns>
+        public static List<Modification> GetModificationsFromFullSequence(string fullSequence,
+            Dictionary<string, Modification> allModsKnown) => [.. GetModificationDictionaryFromFullSequence(fullSequence, allModsKnown).Values];
     }
 }
diff --git a/mzLib/Proteomics/AminoAcidPolymer/AminoAcidPolymer.cs b/mzLib/Proteomics/AminoAcidPolymer/AminoAcidPolymer.cs
index 1d7f1b231..1abb40e99 100644
--- a/mzLib/Proteomics/AminoAcidPolymer/AminoAcidPolymer.cs
+++ b/mzLib/Proteomics/AminoAcidPolymer/AminoAcidPolymer.cs
@@ -1103,7 +1103,7 @@ private void ParseSequence(string sequence)
                         {
                             modification = new OldSchoolChemicalFormulaModification(ChemicalFormula.ParseFormula(modString));
                         }
-                        catch (MzLibException)
+                        catch (MzLibException e)
                         {
                             if (double.TryParse(modString, out double mass))
                             {
@@ -1111,7 +1111,7 @@ private void ParseSequence(string sequence)
                             }
                             else
                             {
-                                throw new MzLibException("Unable to correctly parse the following modification: " + modString);
+                                throw new MzLibException("Unable to correctly parse the following modification: " + modString, e);
                             }
                         }
 
diff --git a/mzLib/Proteomics/ProteolyticDigestion/PeptideWithSetModifications.cs b/mzLib/Proteomics/ProteolyticDigestion/PeptideWithSetModifications.cs
index 8eb6e6bdf..aafec0a5e 100644
--- a/mzLib/Proteomics/ProteolyticDigestion/PeptideWithSetModifications.cs
+++ b/mzLib/Proteomics/ProteolyticDigestion/PeptideWithSetModifications.cs
@@ -69,7 +69,7 @@ public PeptideWithSetModifications(string sequence, Dictionary<string, Modificat
 
             FullSequence = sequence;
             _baseSequence = IBioPolymerWithSetMods.GetBaseSequenceFromFullSequence(sequence);
-            GetModsAfterDeserialization(allKnownMods);
+            _allModsOneIsNterminus = IBioPolymerWithSetMods.GetModificationDictionaryFromFullSequence(sequence, allKnownMods);
             NumFixedMods = numFixedMods;
             _digestionParams = digestionParams as DigestionParams;
             PairedTargetDecoySequence = pairedTargetDecoySequence; 
@@ -910,7 +910,7 @@ public override int GetHashCode()
         /// </summary>
         public void SetNonSerializedPeptideInfo(Dictionary<string, Modification> idToMod, Dictionary<string, Protein> accessionToProtein, DigestionParams dp)
         {
-            GetModsAfterDeserialization(idToMod);
+            _allModsOneIsNterminus = IBioPolymerWithSetMods.GetModificationDictionaryFromFullSequence(FullSequence, idToMod);
             GetProteinAfterDeserialization(accessionToProtein);
             _digestionParams = dp;
         }
@@ -919,66 +919,6 @@ public void SetNonSerializedPeptideInfo(Dictionary<string, Modification> idToMod
             Dictionary<string, Protein> accessionToProtein, IDigestionParams dp) => 
             SetNonSerializedPeptideInfo(idToMod, accessionToProtein, (DigestionParams)dp);
 
-        private void GetModsAfterDeserialization(Dictionary<string, Modification> idToMod)
-        {
-            _allModsOneIsNterminus = new Dictionary<int, Modification>();
-            int currentModStart = 0;
-            int currentModificationLocation = 1;
-            bool currentlyReadingMod = false;
-            int bracketCount = 0;
-
-            for (int r = 0; r < FullSequence.Length; r++)
-            {
-                char c = FullSequence[r];
-                if (c == '[')
-                {
-                    currentlyReadingMod = true;
-                    if (bracketCount == 0)
-                    {
-                        currentModStart = r + 1;
-                    }
-                    bracketCount++;
-                }
-                else if (c == ']')
-                {
-                    string modId = null;
-                    bracketCount--;
-                    if (bracketCount == 0)
-                    {
-                        try
-                        {
-                            //remove the beginning section (e.g. "Fixed", "Variable", "Uniprot")
-                            string modString = FullSequence.Substring(currentModStart, r - currentModStart);
-                            int splitIndex = modString.IndexOf(':');
-                            string modType = modString.Substring(0, splitIndex);
-                            modId = modString.Substring(splitIndex + 1, modString.Length - splitIndex - 1);
-                        }
-                        catch (Exception e)
-                        {
-                            throw new MzLibUtil.MzLibException(
-                                "Error while trying to parse string into peptide: " + e.Message);
-                        }
-                        if (!idToMod.TryGetValue(modId, out Modification mod))
-                        {
-                            throw new MzLibUtil.MzLibException(
-                                "Could not find modification while reading string: " + FullSequence);
-                        }
-                        if (mod.LocationRestriction.Contains("C-terminal.") && r == FullSequence.Length - 1)
-                        {
-                            currentModificationLocation = BaseSequence.Length + 2;
-                        }
-                        _allModsOneIsNterminus.Add(currentModificationLocation, mod);
-                        currentlyReadingMod = false;
-                    }
-                }
-                else if (!currentlyReadingMod)
-                {
-                    currentModificationLocation++;
-                }
-                //else do nothing
-            }
-        }
-
         private void GetProteinAfterDeserialization(Dictionary<string, Protein> idToProtein)
         {
             Protein protein = null;
diff --git a/mzLib/Readers/SearchResults/SpectrumMatchTsvReader.cs b/mzLib/Readers/SearchResults/SpectrumMatchTsvReader.cs
index 62a720c63..709b391ba 100644
--- a/mzLib/Readers/SearchResults/SpectrumMatchTsvReader.cs
+++ b/mzLib/Readers/SearchResults/SpectrumMatchTsvReader.cs
@@ -28,7 +28,7 @@ public static List<SpectrumMatchFromTsv> ReadTsv(string filePath, out List<strin
             }
             catch (Exception e)
             {
-                throw new MzLibException("Could not read file: " + e.Message);
+                throw new MzLibException("Could not read file: " + e.Message, e);
             }
 
             int lineCount = 0;
diff --git a/mzLib/Test/TestPeptideWithSetMods.cs b/mzLib/Test/TestPeptideWithSetMods.cs
index 355d9d27c..64ce5dbc7 100644
--- a/mzLib/Test/TestPeptideWithSetMods.cs
+++ b/mzLib/Test/TestPeptideWithSetMods.cs
@@ -8,6 +8,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using MzLibUtil;
 using Omics;
 using Omics.Digestion;
 using Omics.Fragmentation;
@@ -1181,5 +1182,96 @@ public static void TestPeptideWithSetModsNoParentProtein()
             Assert.AreEqual('-', last.NextAminoAcid);
             Assert.AreEqual('-', last.NextResidue);
         }
+
+        [Test]
+        public static void TestIBioPolymerWithSetModsModificationFromFullSequence()
+        {
+            Dictionary<string, Modification> un = new Dictionary<string, Modification>();
+            var psiModDeserialized = Loaders.LoadPsiMod(Path.Combine(TestContext.CurrentContext.TestDirectory, "PSI-MOD.obo2.xml"));
+            Dictionary<string, int> formalChargesDictionary = Loaders.GetFormalChargesDictionary(psiModDeserialized);
+            List<Modification> UniProtPtms = Loaders.LoadUniprot(Path.Combine(TestContext.CurrentContext.TestDirectory, "ptmlist2.txt"),
+                    formalChargesDictionary).ToList();
+            List<Protein> proteins = ProteinDbLoader.LoadProteinXML(Path.Combine(TestContext.CurrentContext.TestDirectory, "DatabaseTests", "cRAP_databaseGPTMD.xml"),
+                true, DecoyType.None, UniProtPtms, false, new string[] { "exclude_me" }, out un);
+            var allKnownModDict = UniProtPtms.ToDictionary(p => p.IdWithMotif, p => p);
+            var digestionParameters = new DigestionParams(maxModsForPeptides: 3);
+
+            foreach (Protein p in proteins)
+            {
+                List<PeptideWithSetModifications> digestedPeptides =
+                    p.Digest(digestionParameters, [], [], null, null).ToList();
+                // take the most modified peptide by base sequence and ensure all methods function properly
+                foreach (var targetPeptide in digestedPeptides
+                             .Where(pep => pep.FullSequence.Contains('['))
+                             .GroupBy(pep => pep.BaseSequence)
+                             .Select(pepGroup => pepGroup.MaxBy(pep => pep.AllModsOneIsNterminus.Count)))
+                {
+                    var startResidue = targetPeptide.OneBasedStartResidue;
+                    var endResidue = targetPeptide.OneBasedEndResidue;
+
+                    // Pull our expected modifications based upon parent protein object with a maximum value of DigestionParameters.MaxMods
+                    // A bunch of logic to count the number of expected modifications based upon the xml database entries
+                    int expectedModCount = 0;
+                    foreach (var modDictEntry in p.OneBasedPossibleLocalizedModifications
+                                 .Where(mod => mod.Key >= startResidue && mod.Key <= endResidue))
+                    {
+                        if (modDictEntry.Value.Count > 1)
+                        {
+                            var locRestrictions = modDictEntry.Value.Select(mod => mod.LocationRestriction).ToList();
+
+                            if (locRestrictions.AllSame())
+                            {
+                                if (locRestrictions.First() == "Anywhere.")
+                                    expectedModCount++;
+                                else if (locRestrictions.First() == "N-terminal." && modDictEntry.Key == startResidue)
+                                    expectedModCount++;
+                            }
+                            else if (modDictEntry.Value.Select(mod => mod.LocationRestriction).Contains("Anywhere.")
+                                     && modDictEntry.Value.Select(mod => mod.LocationRestriction)
+                                         .Contains("N-terminal."))
+                            {
+                                expectedModCount++;
+                                if (modDictEntry.Key == startResidue)
+                                    expectedModCount++;
+                            }
+                        }
+                        else
+                        {
+                            switch (modDictEntry.Value.First().LocationRestriction)
+                            {
+                                case "Anywhere.":
+                                case "N-terminal." when modDictEntry.Key == startResidue:
+                                    expectedModCount++;
+                                    break;
+                            }
+                        }
+                    }
+
+                    expectedModCount = Math.Min(expectedModCount, digestionParameters.MaxMods);
+
+                    var expectedModifications = p.OneBasedPossibleLocalizedModifications.Where(mod =>
+                        mod.Key >= startResidue &&
+                        mod.Key <= endResidue).SelectMany(mod => mod.Value).ToList();
+
+                    // Parse modifications from PWSM and two IBioPolymerWithSetMods methods
+                    var pwsmModDict = targetPeptide.AllModsOneIsNterminus;
+                    var bpwsmModDict = IBioPolymerWithSetMods.GetModificationDictionaryFromFullSequence(targetPeptide.FullSequence, allKnownModDict);
+                    var bpwsmModList = IBioPolymerWithSetMods.GetModificationsFromFullSequence(targetPeptide.FullSequence, allKnownModDict);
+
+                    // Ensure all methods are in agreement by modification count
+                    Assert.AreEqual(pwsmModDict.Count, expectedModCount);
+                    Assert.AreEqual(bpwsmModDict.Count, expectedModCount);
+                    Assert.AreEqual(bpwsmModList.Count, expectedModCount);
+
+                    // Ensure all methods are in agreement by modification identify
+                    foreach (var pwsmModification in pwsmModDict.Values)
+                        Assert.Contains(pwsmModification, expectedModifications);
+                    foreach (var pwsmModification in bpwsmModDict.Values)
+                        Assert.Contains(pwsmModification, expectedModifications);
+                    foreach (var pwsmModification in bpwsmModList)
+                        Assert.Contains(pwsmModification, expectedModifications);
+                }
+            }
+        }
     }
 }
\ No newline at end of file