diff --git a/src/assembly/problems.jl b/src/assembly/problems.jl
index da3f68d..7c8dd95 100644
--- a/src/assembly/problems.jl
+++ b/src/assembly/problems.jl
@@ -69,15 +69,15 @@ function empty!(assembly::Assembly)
     empty!(assembly.c)
 end
 
-function isempty(assembly::Assembly)
-    T = isempty(assembly.M)
-    T &= isempty(assembly.K)
-    T &= isempty(assembly.Kg)
-    T &= isempty(assembly.f)
-    T &= isempty(assembly.fg)
-    T &= isempty(assembly.C1)
-    T &= isempty(assembly.C2)
-    T &= isempty(assembly.D)
+function Base.isempty(assembly::Assembly)
+    T = Base.isempty(assembly.M)
+    T &= Base.isempty(assembly.K)
+    T &= Base.isempty(assembly.Kg)
+    T &= Base.isempty(assembly.f)
+    T &= Base.isempty(assembly.fg)
+    T &= Base.isempty(assembly.C1)
+    T &= Base.isempty(assembly.C2)
+    T &= Base.isempty(assembly.D)
     T &= isempty(assembly.g)
     T &= isempty(assembly.c)
     return T