diff --git a/src/remake.jl b/src/remake.jl
index bed4a8b5d..9e059329e 100644
--- a/src/remake.jl
+++ b/src/remake.jl
@@ -543,40 +543,76 @@ end
 
 function fill_u0(prob, u0; defs = nothing, use_defaults = false)
     vsyms = variable_symbols(prob)
-    if length(u0) == length(vsyms)
-        return u0
+    sym_to_idx = anydict()
+    idx_to_sym = anydict()
+    idx_to_val = anydict()
+    for (k, v) in u0
+        idx = variable_index(prob, k)
+        idx === nothing && continue
+        sym_to_idx[k] = idx
+        idx_to_sym[idx] = k
+        idx_to_val[idx] = v
     end
-    newvals = anydict()
     for sym in vsyms
-        varmap_has_var(u0, sym) && continue
-        def = if defs === nothing || (defval = varmap_get(defs, sym)) === nothing ||
-                 (symbolic_type(defval) === NotSymbolic() && !use_defaults)
-            nothing
-        else
+        haskey(sym_to_idx, sym) && continue
+        idx = variable_index(prob, sym)
+        haskey(idx_to_val, idx) && continue
+        sym_to_idx[sym] = idx
+        idx_to_sym[idx] = sym
+        idx_to_val[idx] = if defs !== nothing &&
+                             (defval = varmap_get(defs, sym)) !== nothing &&
+                             (symbolic_type(defval) != NotSymbolic() || use_defaults)
             defval
+        else
+            getu(prob, sym)(prob)
         end
-        newvals[sym] = @something def getu(prob, sym)(prob)
     end
-    return merge(u0, newvals)
+    newvals = anydict()
+    for (idx, val) in idx_to_val
+        newvals[idx_to_sym[idx]] = val
+    end
+    for (k, v) in u0
+        haskey(sym_to_idx, k) && continue
+        newvals[k] = v
+    end
+    return newvals
 end
 
 function fill_p(prob, p; defs = nothing, use_defaults = false)
-    psyms = parameter_symbols(prob)::Vector
-    if length(p) == length(psyms)
-        return p
+    psyms = parameter_symbols(prob)
+    sym_to_idx = anydict()
+    idx_to_sym = anydict()
+    idx_to_val = anydict()
+    for (k, v) in p
+        idx = parameter_index(prob, k)
+        idx === nothing && continue
+        sym_to_idx[k] = idx
+        idx_to_sym[idx] = k
+        idx_to_val[idx] = v
     end
-    newvals = anydict()
     for sym in psyms
-        varmap_has_var(p, sym) && continue
-        def = if defs === nothing || (defval = varmap_get(defs, sym)) === nothing ||
-                 (symbolic_type(defval) === NotSymbolic() && !use_defaults)
-            nothing
-        else
+        haskey(sym_to_idx, sym) && continue
+        idx = parameter_index(prob, sym)
+        haskey(idx_to_val, idx) && continue
+        sym_to_idx[sym] = idx
+        idx_to_sym[idx] = sym
+        idx_to_val[idx] = if defs !== nothing &&
+                             (defval = varmap_get(defs, sym)) !== nothing &&
+                             (symbolic_type(defval) != NotSymbolic() || use_defaults)
             defval
+        else
+            getp(prob, sym)(prob)
         end
-        newvals[sym] = @something def getp(prob, sym)(prob)
     end
-    return merge(p, newvals)
+    newvals = anydict()
+    for (idx, val) in idx_to_val
+        newvals[idx_to_sym[idx]] = val
+    end
+    for (k, v) in p
+        haskey(sym_to_idx, k) && continue
+        newvals[k] = v
+    end
+    return newvals
 end
 
 function _updated_u0_p_symmap(prob, u0, ::Val{true}, p, ::Val{false})
diff --git a/test/remake_tests.jl b/test/remake_tests.jl
index ad679bc61..e65f91bd6 100644
--- a/test/remake_tests.jl
+++ b/test/remake_tests.jl
@@ -295,3 +295,22 @@ a = Remake_Test1(p = 1)
 @test @inferred remake(a, p = 2) == Remake_Test1(p = 2)
 @test @inferred remake(a, args = 1) == Remake_Test1(1, p = 1)
 @test @inferred remake(a, kwargs = (; a = 1)) == Remake_Test1(p = 1, a = 1)
+
+@testset "fill_u0 and fill_p ignore identical variables with different names" begin
+    sys = SymbolCache(Dict(:x => 1, :x2 => 1, :y => 2), Dict(:a => 1, :a2 => 1, :b => 2),
+        :t; defaults = Dict(:x => 1, :y => 2, :a => 3, :b => 4))
+    function foo(du, u, p, t)
+        du .= u .* p
+    end
+    prob = ODEProblem(ODEFunction(foo; sys), [1.5, 2.5], (0.0, 1.0), [3.5, 4.5])
+    u0 = Dict(:x2 => 2)
+    newu0 = SciMLBase.fill_u0(prob, u0; defs = default_values(sys))
+    @test length(newu0) == 2
+    @test get(newu0, :x2, 0) == 2
+    @test get(newu0, :y, 0) == 2.5
+    p = Dict(:a2 => 3)
+    newp = SciMLBase.fill_p(prob, p; defs = default_values(sys))
+    @test length(newp) == 2
+    @test get(newp, :a2, 0) == 3
+    @test get(newp, :b, 0) == 4.5
+end