diff --git a/src/Main/Base/Project/Src/Services/HelpProvider.cs b/src/Main/Base/Project/Src/Services/HelpProvider.cs
index eb923d6d1b..95c4bf0007 100644
--- a/src/Main/Base/Project/Src/Services/HelpProvider.cs
+++ b/src/Main/Base/Project/Src/Services/HelpProvider.cs
@@ -21,6 +21,8 @@ namespace ICSharpCode.SharpDevelop
 		
 		public static void ShowHelp(IClass c)
 		{
+			if (c == null)
+				throw new ArgumentNullException("c");
 			foreach (HelpProvider p in GetProviders()) {
 				if (p.TryShowHelp(c))
 					return;
@@ -35,6 +37,8 @@ namespace ICSharpCode.SharpDevelop
 		
 		public static void ShowHelp(IMember m)
 		{
+			if (m == null)
+				throw new ArgumentNullException("m");
 			foreach (HelpProvider p in GetProviders()) {
 				if (p.TryShowHelp(m))
 					return;
@@ -44,11 +48,17 @@ namespace ICSharpCode.SharpDevelop
 		
 		public virtual bool TryShowHelp(IMember m)
 		{
-			return TryShowHelp(m.FullyQualifiedName);
+			IMethod method = m as IMethod;
+			if (method != null && method.IsConstructor)
+				return TryShowHelp(m.DeclaringType.FullyQualifiedName + "." + m.DeclaringType.Name);
+			else
+				return TryShowHelp(m.FullyQualifiedName);
 		}
 		
 		public static void ShowHelp(string fullTypeName)
 		{
+			if (fullTypeName == null)
+				throw new ArgumentNullException("fullTypeName");
 			foreach (HelpProvider p in GetProviders()) {
 				if (p.TryShowHelp(fullTypeName))
 					return;
@@ -64,6 +74,8 @@ namespace ICSharpCode.SharpDevelop
 		
 		public static void ShowHelpByKeyword(string keyword)
 		{
+			if (keyword == null)
+				throw new ArgumentNullException("keyword");
 			foreach (HelpProvider p in GetProviders()) {
 				if (p.TryShowHelpByKeyword(keyword))
 					return;