diff --git a/pwiz_tools/Skyline/FileUI/PeptideSearch/BuildPeptideSearchLibraryControl.cs b/pwiz_tools/Skyline/FileUI/PeptideSearch/BuildPeptideSearchLibraryControl.cs
index 0c9e71d55f..a7f777c4c6 100644
--- a/pwiz_tools/Skyline/FileUI/PeptideSearch/BuildPeptideSearchLibraryControl.cs
+++ b/pwiz_tools/Skyline/FileUI/PeptideSearch/BuildPeptideSearchLibraryControl.cs
@@ -281,11 +281,40 @@ public void AddSearchFiles(IEnumerable<string> fileNames)
             SearchFilenames = BuildLibraryDlg.AddInputFiles(WizardForm, SearchFilenames, fileNames, PerformDDASearch);
         }
 
+        // For test purposes, lets us test error handling
+        public string CutOffScoreText
+        {
+            set { textCutoff.Text = value; } // Can be a null or empty string under some circumstances
+        }
+
+        public bool NeedsCutoffScore => comboInputFileType.SelectedIndex > 0; // Only needed if Skyline is conducting the search
+
+        private double? _cutoffScore; // May be null when Skyline is not doing the search
+
         public double? CutOffScore
         {
             // Only valid when Skyline performs the search
-            get { return comboInputFileType.SelectedIndex > 0 ? double.Parse(textCutoff.Text) : (double?) null; }
-            set { textCutoff.Text = value.HasValue ? value.Value.ToString(CultureInfo.CurrentCulture) : string.Empty; }
+            get { return NeedsCutoffScore ? _cutoffScore : null; }
+            set
+            {
+                _cutoffScore = value;
+                textCutoff.Text = _cutoffScore.HasValue ? _cutoffScore.Value.ToString(CultureInfo.CurrentCulture) : string.Empty;
+            }
+        }
+
+        public bool ValidateCutoffScore()
+        {
+            if (!NeedsCutoffScore)
+            {
+                return true; // Doesn't matter what's in the text box, we won't use it
+            }
+            var helper = new MessageBoxHelper(this.ParentForm);
+            if (helper.ValidateDecimalTextBox(textCutoff, out var cutoffScore))
+            {
+                _cutoffScore = cutoffScore;
+                return true;
+            }
+            return false;
         }
 
         public bool IncludeAmbiguousMatches
@@ -643,5 +672,6 @@ private void comboInputFileType_SelectedIndexChanged(object sender, EventArgs e)
         {
             UpdatePerformDDASearch();
         }
+
     }
 }
diff --git a/pwiz_tools/Skyline/FileUI/PeptideSearch/ImportPeptideSearchDlg.cs b/pwiz_tools/Skyline/FileUI/PeptideSearch/ImportPeptideSearchDlg.cs
index 016ae5432c..2a48854399 100644
--- a/pwiz_tools/Skyline/FileUI/PeptideSearch/ImportPeptideSearchDlg.cs
+++ b/pwiz_tools/Skyline/FileUI/PeptideSearch/ImportPeptideSearchDlg.cs
@@ -485,6 +485,10 @@ private void NextPage()
                     {
                         _pagesToSkip.Clear();
 
+                        if (!BuildPepSearchLibControl.ValidateCutoffScore())
+                        {
+                            return;
+                        }
                         ImportPeptideSearch.IsDDASearch = BuildPepSearchLibControl.PerformDDASearch;
                         ImportFastaControl.IsDDASearch = BuildPepSearchLibControl.PerformDDASearch;
                         if (!BuildPepSearchLibControl.UseExistingLibrary)
diff --git a/pwiz_tools/Skyline/TestFunctional/DdaSearchTest.cs b/pwiz_tools/Skyline/TestFunctional/DdaSearchTest.cs
index f55f7bd97f..caf2b86f99 100644
--- a/pwiz_tools/Skyline/TestFunctional/DdaSearchTest.cs
+++ b/pwiz_tools/Skyline/TestFunctional/DdaSearchTest.cs
@@ -224,17 +224,24 @@ private void TestSearch()
             // Add the test xml file to the search files list and try to 
             // build the document library.
 
-            RunUI(() =>
+            var errMsgDlg = ShowDialog<MessageDlg>(() =>
             {
                 Assert.IsTrue(importPeptideSearchDlg.CurrentPage == ImportPeptideSearchDlg.Pages.spectra_page);
                 importPeptideSearchDlg.BuildPepSearchLibControl.PerformDDASearch = true;
                 importPeptideSearchDlg.BuildPepSearchLibControl.DdaSearchDataSources = SearchFiles.Select(o => (MsDataFileUri)new MsDataFilePath(o)).Take(1).ToArray();
                 importPeptideSearchDlg.BuildPepSearchLibControl.WorkflowType = ImportPeptideSearchDlg.Workflow.dia; // will go back and switch to DDA
-                importPeptideSearchDlg.BuildPepSearchLibControl.CutOffScore = 0.9;
+                importPeptideSearchDlg.BuildPepSearchLibControl.CutOffScoreText = @"12%"; // Intentionally bad 
                 importPeptideSearchDlg.BuildPepSearchLibControl.IrtStandards = IrtStandard.AUTO;
                 Assert.IsTrue(importPeptideSearchDlg.ClickNextButton());
             });
+            OkDialog(errMsgDlg, errMsgDlg.OkDialog); // Expect complaint about bad cutoff score
 
+            RunUI(() =>
+            {
+                Assert.IsTrue(importPeptideSearchDlg.CurrentPage == ImportPeptideSearchDlg.Pages.spectra_page); // Should not have advanced
+                importPeptideSearchDlg.BuildPepSearchLibControl.CutOffScore = 0.9;
+                Assert.IsTrue(importPeptideSearchDlg.ClickNextButton());
+            });
             // With only 1 source, no add/remove prefix/suffix dialog
 
             // We're on the "Match Modifications" page. Add M+16 mod.