diff --git a/SourceGen/DisasmProject.cs b/SourceGen/DisasmProject.cs
index 7a87a46..2effea4 100644
--- a/SourceGen/DisasmProject.cs
+++ b/SourceGen/DisasmProject.cs
@@ -664,6 +664,22 @@ namespace SourceGen {
             }
         }
 
+        private void ValidateAddressMap() {
+            foreach (AddressMap.AddressMapEntry entry in AddrMap) {
+                if ((entry.Addr & 0xff0000) != ((entry.Addr + entry.Length - 1) & 0xff0000)) {
+                    string fmt = Res.Strings.MSG_BANK_OVERRUN_DETAIL_FMT;
+                    int firstNext = (entry.Addr & 0xff0000) + 0x010000;
+                    int badOffset = entry.Offset + (firstNext - entry.Addr);
+                    Messages.Add(new MessageList.MessageEntry(
+                        MessageList.MessageEntry.SeverityLevel.Error,
+                        entry.Offset,
+                        MessageList.MessageEntry.MessageType.BankOverrun,
+                        string.Format(fmt, "+" + badOffset.ToString("x6")),
+                        MessageList.MessageEntry.ProblemResolution.None));
+                }
+            }
+        }
+
         #region Analysis
 
         /// <summary>
@@ -809,6 +825,7 @@ namespace SourceGen {
             Validate();
             reanalysisTimer.EndTask("Validate");
 #endif
+            ValidateAddressMap();
 
             reanalysisTimer.EndTask("DisasmProject.Analyze()");
             //reanalysisTimer.DumpTimes("DisasmProject timers:", debugLog);
diff --git a/SourceGen/MessageList.cs b/SourceGen/MessageList.cs
index 30c9147..4df60ed 100644
--- a/SourceGen/MessageList.cs
+++ b/SourceGen/MessageList.cs
@@ -52,6 +52,7 @@ namespace SourceGen {
                 UnresolvedWeakRef,
                 InvalidOffsetOrLength,
                 InvalidDescriptor,
+                BankOverrun,
             }
             public MessageType MsgType { get; private set; }
 
@@ -163,6 +164,9 @@ namespace SourceGen {
                 case MessageEntry.MessageType.InvalidDescriptor:
                     problem = Res.Strings.MSG_INVALID_DESCRIPTOR;
                     break;
+                case MessageEntry.MessageType.BankOverrun:
+                    problem = Res.Strings.MSG_BANK_OVERRUN;
+                    break;
                 default:
                     problem = "???";
                     break;
diff --git a/SourceGen/Res/Strings.xaml b/SourceGen/Res/Strings.xaml
index 945d675..911ddf1 100644
--- a/SourceGen/Res/Strings.xaml
+++ b/SourceGen/Res/Strings.xaml
@@ -107,6 +107,8 @@ limitations under the License.
     <system:String x:Key="str_InvalidFormatWordSelUnevenFmt">Unable to format as word: each selected region must have an even number of bytes ({0} region(s) are selected).</system:String>
     <system:String x:Key="str_LocalVariableTableClear">• Clear variables</system:String>
     <system:String x:Key="str_LocalVariableTableEmpty">• Empty variable table</system:String>
+    <system:String x:Key="str_MsgBankOverrun">Address bank overrun</system:String>
+    <system:String x:Key="str_MsgBankOverrunDetailFmt">Bank boundary crossed at offset {0}</system:String>
     <system:String x:Key="str_MsgFormatDescriptorIgnored">Format ignored</system:String>
     <system:String x:Key="str_MsgHiddenLabel">Hidden label</system:String>
     <system:String x:Key="str_MsgHiddenLocalVariableTable">Hidden variable table</system:String>
diff --git a/SourceGen/Res/Strings.xaml.cs b/SourceGen/Res/Strings.xaml.cs
index 31ddbe8..eb3e5ea 100644
--- a/SourceGen/Res/Strings.xaml.cs
+++ b/SourceGen/Res/Strings.xaml.cs
@@ -195,6 +195,10 @@ namespace SourceGen.Res {
             (string)Application.Current.FindResource("str_LocalVariableTableClear");
         public static string LOCAL_VARIABLE_TABLE_EMPTY =
             (string)Application.Current.FindResource("str_LocalVariableTableEmpty");
+        public static string MSG_BANK_OVERRUN =
+            (string)Application.Current.FindResource("str_MsgBankOverrun");
+        public static string MSG_BANK_OVERRUN_DETAIL_FMT =
+            (string)Application.Current.FindResource("str_MsgBankOverrunDetailFmt");
         public static string MSG_FORMAT_DESCRIPTOR_IGNORED =
             (string)Application.Current.FindResource("str_MsgFormatDescriptorIgnored");
         public static string MSG_HIDDEN_LABEL =