diff --git a/src/RecursiveApply/RecursiveApply.jl b/src/RecursiveApply/RecursiveApply.jl
index f57b3105da..4ab5c6a43c 100755
--- a/src/RecursiveApply/RecursiveApply.jl
+++ b/src/RecursiveApply/RecursiveApply.jl
@@ -67,8 +67,30 @@ rmap(fn::F, X::Tuple, Y) where {F} =
     (rmap(fn, first(X), Y), rmap(fn, Base.tail(X), Y)...)
 
 function rmap(fn::F, X::NamedTuple, Y::NamedTuple) where {F}
-    @assert nt_names(X) === nt_names(Y)
-    return NamedTuple{nt_names(X)}(rmap(fn, Tuple(X), Tuple(Y)))
+    # @assert nt_names(X) === nt_names(Y)
+    # return NamedTuple{nt_names(X)}(rmap(fn, Tuple(X), Tuple(Y)))
+    x_names = nt_names(X)
+    y_names = nt_names(Y)
+    
+    # Check if Y names are a subset of X names
+    if !issubset(y_names, x_names)
+        throw(ArgumentError("Names in Y must be a subset of names in X. Y has names: $y_names, X has names: $x_names"))
+    end
+    
+    # Create a new NamedTuple with the same structure as X
+    # For matching names, apply fn to the corresponding values
+    # For non-matching names, keep the original values from X
+    result_values = map(x_names) do name
+        if name in y_names
+            # Apply fn to the matching values
+            rmap(fn, getproperty(X, name), getproperty(Y, name))
+        else
+            # Keep the original value from X
+            getproperty(X, name)
+        end
+    end
+    
+    return NamedTuple{x_names}(result_values)
 end
 rmap(fn::F, X::NamedTuple, Y) where {F} =
     NamedTuple{nt_names(X)}(rmap(fn, Tuple(X), Y))
diff --git a/test/RecursiveApply/unit_recursive_apply.jl b/test/RecursiveApply/unit_recursive_apply.jl
index 1ccc7cf49f..ee65183632 100644
--- a/test/RecursiveApply/unit_recursive_apply.jl
+++ b/test/RecursiveApply/unit_recursive_apply.jl
@@ -1,6 +1,7 @@
 using JET
 using Test
 
+import ClimaCore as CC
 using ClimaCore.RecursiveApply
 using ClimaCore.Geometry
 
@@ -98,3 +99,53 @@ end
     @test rz.b.u == 2
     @test rz.b.v == 4
 end
+
+@testset "NamedTuple subset functionality" begin
+    # Test basic subset functionality
+    X = (a=1, b=2.0, d=[1, 2, 3])
+    Y = (a=10, b=3.0)
+    
+    result = RecursiveApply.rmap(+, X, Y)
+    @test result.a == 11  # 1 + 10
+    @test result.b == 5.0  # 2.0 + 3.0
+    @test result.d == [1, 2, 3]  # unchanged from X
+    
+    # Test with nested NamedTuples
+    X_nested = (a=(x=1, y=2), b=(z=3, w=4))
+    Y_nested = (a=(x=10,),)
+    
+    result_nested = RecursiveApply.rmap(+, X_nested, Y_nested)
+    @test result_nested.a.x == 11  # 1 + 10
+    @test result_nested.a.y == 2  # unchanged from X
+    @test result_nested.b.z == 3  # unchanged from X
+    @test result_nested.b.w == 4  # unchanged from X
+    
+    # Test error case (Y has names not in X)
+    Y_error = (a=1, e=5)  # 'e' is not in X
+    @test_throws ArgumentError RecursiveApply.rmap(+, X, Y_error)
+    
+    # Test type stability
+    @test_opt RecursiveApply.rmap(+, X, Y)
+    @test_opt RecursiveApply.rmap(+, X_nested, Y_nested)
+
+    FT = Float64
+    domain = CC.Domains.IntervalDomain(
+        CC.Geometry.ZPoint{FT}(0),
+        CC.Geometry.ZPoint{FT}(1),
+        boundary_names = (:bottom, :top),
+    )
+    mesh = CC.Meshes.IntervalMesh(domain, nelems = 2)
+    space = CC.Spaces.CenterFiniteDifferenceSpace(mesh)
+    coord = CC.Fields.coordinate_field(space)
+
+    X_nt = (; a = 1.0, b = 2.0, c = 3.0)
+    X_field = map(Returns(X_nt), coord)
+
+    Y_nt = (; a = 10.0, b = 3.0)
+    Y_field = map(Returns(Y_nt), coord)
+
+    result_field = @. RecursiveApply.rmap(+, X_field, Y_field)
+    @test all(==(11.0), parent(result_field.a))
+    @test all(==(5.0), parent(result_field.b))
+    @test all(==(3.0), parent(result_field.c))
+end