diff --git a/src/assemble.jl b/src/assemble.jl
index b60a8b6..a2bfd55 100644
--- a/src/assemble.jl
+++ b/src/assemble.jl
@@ -61,6 +61,8 @@ function mt_assemble(data::AbstractVector{<:AbstractData}, basis)
     _prog_ctr = 0
     next = 1
 
+    failed = Int[] 
+
     Threads.@threads for _i = 1:nthreads() 
 
         while next <= length(packets)
@@ -69,25 +71,36 @@ function mt_assemble(data::AbstractVector{<:AbstractData}, basis)
                 break
             end
             lock(_lock)
-            p = packets[next]
+            cur = next 
             next += 1
             unlock(_lock)
+            if cur > length(packets)
+                break 
+            end 
+            p = packets[cur]
 
             # assemble the corresponding data 
-            Ap = feature_matrix(p.data, basis)
-            Yp = target_vector(p.data)
-            Wp = weight_vector(p.data)
+            try 
+                Ap = feature_matrix(p.data, basis)
+                Yp = target_vector(p.data)
+                Wp = weight_vector(p.data)
 
-            # write into global design matrix 
-            lock(_lock)
-            A[p.rows, :] .= Ap 
-            Y[p.rows] .= Yp
-            W[p.rows] .= Wp
-            _prog_ctr += length(p.rows)
-            ProgressMeter.update!(_prog, _prog_ctr)
-            unlock(_lock)
+                # write into global design matrix 
+                lock(_lock)
+                A[p.rows, :] .= Ap 
+                Y[p.rows] .= Yp
+                W[p.rows] .= Wp
+                _prog_ctr += length(p.rows)
+                ProgressMeter.update!(_prog, _prog_ctr)
+                unlock(_lock)
+            catch 
+                @info("failed assembly: cur = $cur")
+                push!(failed, cur)
+            end
         end
+        @info("thread $_i done")
     end
     @info "  - Assembly completed."
+    @show failed 
     return Array(A), Array(Y), Array(W)
 end