diff --git a/classpath/ikvm/internal/WeakIdentityMap.java b/classpath/ikvm/internal/WeakIdentityMap.java
index 944fc1db..b6a203a0 100644
--- a/classpath/ikvm/internal/WeakIdentityMap.java
+++ b/classpath/ikvm/internal/WeakIdentityMap.java
@@ -59,6 +59,11 @@ public final class WeakIdentityMap
     {
         if (key == null)
             throw new NullPointerException();
+        putImpl(key, value, true);
+    }
+
+    private void putImpl(Object key, Object value, boolean tryGC)
+    {
         int emptySlot = -1;
         int keySlot = -1;
         for (int i = 0; i < keys.length; i++)
@@ -85,6 +90,12 @@ public final class WeakIdentityMap
         }
         else
         {
+            if (tryGC)
+            {
+                GC.Collect(0);
+                putImpl(key, value, false);
+                return;
+            }
             int len = keys.length;
             WeakReference[] newkeys = new WeakReference[len * 2];
             Object[] newvalues = new Object[newkeys.length];
diff --git a/runtime/ByteCode.cs b/runtime/ByteCode.cs
index 54cb4df7..46ecf69f 100644
--- a/runtime/ByteCode.cs
+++ b/runtime/ByteCode.cs
@@ -379,6 +379,7 @@ enum NormalizedByteCode : byte
 	__ifnull = 198,
 	__ifnonnull = 199,
 	// This is where the pseudo-bytecodes start
+	__athrow_no_unmap = 244,
 	__dynamic_getstatic = 245,
 	__dynamic_putstatic = 246,
 	__dynamic_getfield = 247,
diff --git a/runtime/ClassFile.cs b/runtime/ClassFile.cs
index 8e2e5874..b941a3e1 100644
--- a/runtime/ClassFile.cs
+++ b/runtime/ClassFile.cs
@@ -2497,6 +2497,14 @@ namespace IKVM.Internal
 					}
 				}
 
+				internal bool IsBranchTarget
+				{
+					get
+					{
+						return (flags & InstructionFlags.BranchTarget) != 0;
+					}
+				}
+
 				internal void PatchOpCode(NormalizedByteCode bc)
 				{
 					this.normopcode = bc;
diff --git a/runtime/compiler.cs b/runtime/compiler.cs
index 36097678..e1e20e1d 100644
--- a/runtime/compiler.cs
+++ b/runtime/compiler.cs
@@ -1382,7 +1382,7 @@ class Compiler
 			// if there was a forward branch to this instruction, it is forward reachable
 			instructionIsForwardReachable |= block.HasLabel(i);
 
-			if(block.HasLabel(i) || (instr.flags & ClassFile.Method.InstructionFlags.BranchTarget) != 0)
+			if(block.HasLabel(i) || instr.IsBranchTarget)
 			{
 				block.MarkLabel(i);
 			}
@@ -1714,6 +1714,10 @@ class Compiler
 									&& thisType.GetMethodWrapper("fillInStackTrace", "()Ljava.lang.Throwable;", true).DeclaringType == java_lang_Throwable)
 								{
 									ilGenerator.Emit(OpCodes.Call, suppressFillInStackTraceMethod);
+									if(!code[i + 1].IsBranchTarget)
+									{
+										code[i + 1].PatchOpCode(NormalizedByteCode.__athrow_no_unmap);
+									}
 								}
 							}
 							method.EmitNewobj(ilGenerator);
@@ -2766,8 +2770,14 @@ class Compiler
 				case NormalizedByteCode.__monitorexit:
 					ilGenerator.Emit(OpCodes.Call, monitorExitMethod);
 					break;
+				case NormalizedByteCode.__athrow_no_unmap:
+					if(ma.GetRawStackTypeWrapper(i, 0).IsUnloadable)
+					{
+						ilGenerator.Emit(OpCodes.Castclass, typeof(Exception));
+					}
+					ilGenerator.Emit(OpCodes.Throw);
+					break;
 				case NormalizedByteCode.__athrow:
-					// TODO we shouldn't call unmap when we know it isn't needed
 					if(ma.GetRawStackTypeWrapper(i, 0).IsUnloadable)
 					{
 						ilGenerator.Emit(OpCodes.Castclass, typeof(Exception));
@@ -2948,6 +2958,7 @@ class Compiler
 				case NormalizedByteCode.__areturn:
 				case NormalizedByteCode.__return:
 				case NormalizedByteCode.__athrow:
+				case NormalizedByteCode.__athrow_no_unmap:
 				case NormalizedByteCode.__static_error:
 					instructionIsForwardReachable = false;
 					break;