diff --git a/src/operators/mpoham.jl b/src/operators/mpoham.jl
index c25a7c0..cae1b63 100644
--- a/src/operators/mpoham.jl
+++ b/src/operators/mpoham.jl
@@ -82,10 +82,19 @@ function deduce_pspaces(opps::SumOfLocalOperators)
         end
     end
 
-    non_deduced = map(ismissing, pspaces)
-    any(non_deduced) &&
-        error("cannot automatically deduce physical spaces at $(findall(non_deduced))")
+    not_missing = filter(!ismissing, pspaces)
 
+    if length(not_missing) != length(pspaces) # Some spaces were not defined / not able to be deduced
+        if allequal(not_missing) # all non-missing spaces are equal
+            # fill in the missing spaces with the unique non-missing space
+            uniquespace = first(not_missing)
+            for i in eachindex(pspaces)
+                pspaces[i] = uniquespace
+            end
+        else # Not all non-missing spaces are equal
+            error("cannot automatically deduce physical spaces at $(findall(map(ismissing, pspaces)))")
+        end
+    end
     return collect(S, pspaces)
 end
 
diff --git a/test/mpoham.jl b/test/mpoham.jl
index 4251f6a..bb4884e 100644
--- a/test/mpoham.jl
+++ b/test/mpoham.jl
@@ -1,4 +1,4 @@
-using MPSKitModels
+using MPSKitModels, MPSKit, TensorKit
 
 lattice = InfiniteChain(1)
 H1 = @mpoham begin
@@ -20,3 +20,13 @@ end
     H = @mpoham sum(ZZ{i,j} for (i, j) in nearest_neighbours(lattice))
     @test length(H) == length(lattice)
 end
+
+@testset "deduce_pspaces" begin
+    # Not fully defining the pspaces should still work
+    lattice = FiniteChain(5)
+    H = @mpoham S_zz(){lattice[2],lattice[3]}
+
+    @test unique(MPSKit.physicalspace(H))[1] == ComplexSpace(2)
+
+    @test_throws Exception @mpoham σˣ(){lattice[1]} + σˣ(; spin=3 // 2){lattice[2]}
+end