diff --git a/CHANGES.txt b/CHANGES.txt
index da6219ac1..c9a83c513 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -10,6 +10,8 @@ Fixes:
 - Issue 15: "Ability to rename projects"
 - Issue 16: "Column name collision when adding data from Freebase"
 - Issue 28: "mql-like preview is not properly unquoting numbers"
+- Issue 45: "Renaming Cells with Ctrl-Enter produced ERROR"
+  Tentative fix for a concurrent bug.
 
 Changes:
 - Moved unit tests from JUnit to TestNG
diff --git a/src/main/java/com/metaweb/gridworks/history/History.java b/src/main/java/com/metaweb/gridworks/history/History.java
index 227276549..bc600bd87 100644
--- a/src/main/java/com/metaweb/gridworks/history/History.java
+++ b/src/main/java/com/metaweb/gridworks/history/History.java
@@ -89,7 +89,7 @@ public class History implements Jsonizable {
         _futureEntries = new ArrayList<HistoryEntry>();
     }
     
-    public void addEntry(HistoryEntry entry) {
+    synchronized public void addEntry(HistoryEntry entry) {
         entry.apply(ProjectManager.singleton.getProject(_projectID));
         _pastEntries.add(entry);
         
@@ -113,7 +113,7 @@ public class History implements Jsonizable {
         ProjectManager.singleton.getProjectMetadata(_projectID).updateModified();
     }
     
-    public List<HistoryEntry> getLastPastEntries(int count) {
+    synchronized public List<HistoryEntry> getLastPastEntries(int count) {
         if (count <= 0) {
             return new LinkedList<HistoryEntry>(_pastEntries);
         } else {
@@ -121,7 +121,7 @@ public class History implements Jsonizable {
         }
     }
     
-    public void undoRedo(long lastDoneEntryID) {
+    synchronized public void undoRedo(long lastDoneEntryID) {
         if (lastDoneEntryID == 0) {
             // undo all the way back to the start of the project
             undo(_pastEntries.size());
@@ -142,7 +142,7 @@ public class History implements Jsonizable {
         }
     }
     
-    public long getPrecedingEntryID(long entryID) {
+    synchronized public long getPrecedingEntryID(long entryID) {
         if (entryID == 0) {
             return -1;
         } else {
@@ -214,7 +214,7 @@ public class History implements Jsonizable {
         }
     }
     
-    public void write(JSONWriter writer, Properties options)
+    synchronized public void write(JSONWriter writer, Properties options)
             throws JSONException {
         
         writer.object();
@@ -234,7 +234,7 @@ public class History implements Jsonizable {
         writer.endObject();
     }
     
-    public void save(Writer writer, Properties options) throws IOException {
+    synchronized public void save(Writer writer, Properties options) throws IOException {
         writer.write("pastEntryCount="); writer.write(Integer.toString(_pastEntries.size())); writer.write('\n');
         for (HistoryEntry entry : _pastEntries) {
             entry.save(writer, options); writer.write('\n');
@@ -248,7 +248,7 @@ public class History implements Jsonizable {
         writer.write("/e/\n");
     }
     
-    public void load(Project project, LineNumberReader reader) throws Exception {
+    synchronized public void load(Project project, LineNumberReader reader) throws Exception {
         String line;
         while ((line = reader.readLine()) != null && !"/e/".equals(line)) {
             int equal = line.indexOf('=');
diff --git a/src/main/java/com/metaweb/gridworks/model/ColumnModel.java b/src/main/java/com/metaweb/gridworks/model/ColumnModel.java
index aae16af73..e3b9b95c2 100644
--- a/src/main/java/com/metaweb/gridworks/model/ColumnModel.java
+++ b/src/main/java/com/metaweb/gridworks/model/ColumnModel.java
@@ -34,7 +34,7 @@ public class ColumnModel implements Jsonizable {
         internalInitialize();
     }
     
-    public void setMaxCellIndex(int maxCellIndex) {
+    synchronized public void setMaxCellIndex(int maxCellIndex) {
         this._maxCellIndex = Math.max(this._maxCellIndex, maxCellIndex);
     }
 
@@ -42,7 +42,7 @@ public class ColumnModel implements Jsonizable {
         return _maxCellIndex;
     }
 
-    public int allocateNewCellIndex() {
+    synchronized public int allocateNewCellIndex() {
         return ++_maxCellIndex;
     }
     
@@ -55,7 +55,7 @@ public class ColumnModel implements Jsonizable {
         return _keyColumnIndex;
     }
     
-    public void addColumnGroup(int startColumnIndex, int span, int keyColumnIndex) {
+    synchronized public void addColumnGroup(int startColumnIndex, int span, int keyColumnIndex) {
         for (ColumnGroup g : columnGroups) {
             if (g.startColumnIndex == startColumnIndex && g.columnSpan == span) {
                 if (g.keyColumnIndex == keyColumnIndex) {
@@ -102,11 +102,11 @@ public class ColumnModel implements Jsonizable {
 		_nameToColumn.put(name, column); // so the next call can check
     }
     
-    public Column getColumnByName(String name) {
+    synchronized public Column getColumnByName(String name) {
         return _nameToColumn.get(name);
     }
     
-    public int getColumnIndexByName(String name) {
+    synchronized public int getColumnIndexByName(String name) {
         for (int i = 0; i < _columnNames.size(); i++) {
             String s = _columnNames.get(i);
             if (name.equals(s)) {
@@ -116,15 +116,15 @@ public class ColumnModel implements Jsonizable {
         return -1;
     }
     
-    public Column getColumnByCellIndex(int cellIndex) {
+    synchronized public Column getColumnByCellIndex(int cellIndex) {
         return _cellIndexToColumn.get(cellIndex);
     }
     
-    public List<String> getColumnNames() {
+    synchronized public List<String> getColumnNames() {
         return _columnNames;
     }
 
-    public void write(JSONWriter writer, Properties options)
+    synchronized public void write(JSONWriter writer, Properties options)
             throws JSONException {
         
         writer.object();
@@ -153,7 +153,7 @@ public class ColumnModel implements Jsonizable {
         writer.endObject();
     }
     
-    public void save(Writer writer, Properties options) throws IOException {
+    synchronized public void save(Writer writer, Properties options) throws IOException {
         writer.write("maxCellIndex="); writer.write(Integer.toString(_maxCellIndex)); writer.write('\n');
         writer.write("keyColumnIndex="); writer.write(Integer.toString(_keyColumnIndex)); writer.write('\n');
 
@@ -170,7 +170,7 @@ public class ColumnModel implements Jsonizable {
         writer.write("/e/\n");
     }
 
-    public void load(LineNumberReader reader) throws Exception {
+    synchronized public void load(LineNumberReader reader) throws Exception {
         String line;
         while ((line = reader.readLine()) != null && !"/e/".equals(line)) {
             int equal = line.indexOf('=');
@@ -199,7 +199,7 @@ public class ColumnModel implements Jsonizable {
         internalInitialize();
     }
     
-    protected void internalInitialize() {
+    synchronized protected void internalInitialize() {
         generateMaps();
         
         // Turn the flat list of column groups into a tree
diff --git a/src/main/java/com/metaweb/gridworks/model/Project.java b/src/main/java/com/metaweb/gridworks/model/Project.java
index db819f20a..15ac364a6 100644
--- a/src/main/java/com/metaweb/gridworks/model/Project.java
+++ b/src/main/java/com/metaweb/gridworks/model/Project.java
@@ -62,7 +62,7 @@ public class Project {
         return ProjectManager.singleton.getProjectMetadata(id);
     }
     
-    public void save() {
+    synchronized public void save() {
         synchronized (this) {
             File dir = ProjectManager.singleton.getProjectDir(id);
             
@@ -257,7 +257,7 @@ public class Project {
         int     keyCellIndex;
     }
     
-    public void recomputeRowContextDependencies() {
+    synchronized public void recomputeRowContextDependencies() {
         List<Group> keyedGroups = new ArrayList<Group>();
         
         addRootKeyedGroup(keyedGroups);