diff --git a/AdjustableModPanel.version b/AdjustableModPanel.version
index 58d2815..55cd351 100644
--- a/AdjustableModPanel.version
+++ b/AdjustableModPanel.version
@@ -9,7 +9,7 @@
     "VERSION": {
         "MAJOR": 1,
         "MINOR": 5,
-        "PATCH": 3,
+        "PATCH": 4,
         "BUILD": 0
     },
     "KSP_VERSION": {
diff --git a/ModPanelComponent.cs b/ModPanelComponent.cs
index 57b7ff4..cbcd7e3 100644
--- a/ModPanelComponent.cs
+++ b/ModPanelComponent.cs
@@ -24,6 +24,7 @@ OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
 
+using System.Linq;
 using UnityEngine;
 
 namespace AdjustableModPanel {
@@ -89,7 +90,14 @@ public void Update () {
         if (texture == null)
           continue;
 
-        var func = button.onTrue.GetInvocationList ()[1];
+        // try any non-null callback in order
+        var func = new Callback[] { button.onTrue, button.onHover, button.onLeftClick, button.onEnable, button.onFalse, button.onHoverOut, button.onDisable }
+          .Select(cb => cb.GetInvocationList().Skip(1).FirstOrDefault()).Where(m => m != null).FirstOrDefault();
+
+        // button with no callbacks. Ignore.
+        if (func == null)
+          continue;
+
         var method = func.Method.Name;
         var module = func.Method.Module.Name;
         if (module.EndsWith (".dll"))
diff --git a/Properties/AssemblyInfo.cs b/Properties/AssemblyInfo.cs
index 4285721..cd03194 100644
--- a/Properties/AssemblyInfo.cs
+++ b/Properties/AssemblyInfo.cs
@@ -10,7 +10,7 @@
 [assembly: AssemblyConfiguration("")]
 [assembly: AssemblyCompany("")]
 [assembly: AssemblyProduct("AdjustableModPanel")]
-[assembly: AssemblyCopyright("Copyright ©  2017-2018")]
+[assembly: AssemblyCopyright("Copyright ©  2017-2019")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
 
@@ -32,5 +32,5 @@
 // You can specify all the values or you can default the Build and Revision Numbers 
 // by using the '*' as shown below:
 // [assembly: AssemblyVersion("1.0.*")]
-[assembly: AssemblyVersion("1.5.3.0")]
-[assembly: AssemblyFileVersion("1.5.3.0")]
+[assembly: AssemblyVersion("1.5.4.0")]
+[assembly: AssemblyFileVersion("1.5.4.0")]