diff --git a/src/systems/parameter_buffer.jl b/src/systems/parameter_buffer.jl
index f2d0867a32..0954d9a40c 100644
--- a/src/systems/parameter_buffer.jl
+++ b/src/systems/parameter_buffer.jl
@@ -721,7 +721,7 @@ end
 
 function Base.showerror(io::IO, e::MissingParametersError)
     println(io, MISSING_PARAMETERS_MESSAGE)
-    println(io, e.vars)
+    println(io, join(e.vars, ", "))
 end
 
 function InvalidParameterSizeException(param, val)
diff --git a/src/systems/problem_utils.jl b/src/systems/problem_utils.jl
index 0be41ea6f7..1f40f61eed 100644
--- a/src/systems/problem_utils.jl
+++ b/src/systems/problem_utils.jl
@@ -752,12 +752,14 @@ function process_SciMLProblem(
 
     u0Type = typeof(u0map)
     pType = typeof(pmap)
-    _u0map = u0map
+
     u0map = to_varmap(u0map, dvs)
     symbols_to_symbolics!(sys, u0map)
-    _pmap = pmap
     pmap = to_varmap(pmap, parameters(sys))
     symbols_to_symbolics!(sys, pmap)
+
+    check_inputmap_keys(sys, u0map, pmap)
+
     defs = add_toterms(recursive_unwrap(defaults(sys)))
     cmap, cs = get_cmap(sys)
     kwargs = NamedTuple(kwargs)
@@ -854,6 +856,43 @@ function process_SciMLProblem(
     implicit_dae ? (f, du0, u0, p) : (f, u0, p)
 end
 
+# Check that the keys of a u0map or pmap are valid
+# (i.e. are symbolic keys, and are defined for the system.)
+function check_inputmap_keys(sys, u0map, pmap)
+    badvarkeys = Any[]
+    for k in keys(u0map)
+        if symbolic_type(k) === NotSymbolic()
+            push!(badvarkeys, k)
+        end
+    end
+
+    badparamkeys = Any[]
+    for k in keys(pmap)
+        if symbolic_type(k) === NotSymbolic()
+            push!(badparamkeys, k)
+        end
+    end
+    (isempty(badvarkeys) && isempty(badparamkeys)) || throw(InvalidKeyError(collect(badvarkeys), collect(badparamkeys)))
+end
+
+const BAD_KEY_MESSAGE = """
+                        Undefined keys found in the parameter or initial condition maps. Check if symbolic variable names have been reassigned. 
+                        The following keys are invalid:
+                        """
+
+struct InvalidKeyError <: Exception
+    vars::Any
+    params::Any
+end
+
+function Base.showerror(io::IO, e::InvalidKeyError) 
+    println(io, BAD_KEY_MESSAGE)
+    println(io, "u0map: $(join(e.vars, ", "))")
+    println(io, "pmap: $(join(e.params, ", "))")
+end
+
+
+
 ##############
 # Legacy functions for backward compatibility
 ##############
diff --git a/test/problem_validation.jl b/test/problem_validation.jl
new file mode 100644
index 0000000000..bce39b51d2
--- /dev/null
+++ b/test/problem_validation.jl
@@ -0,0 +1,34 @@
+using ModelingToolkit
+using ModelingToolkit: t_nounits as t, D_nounits as D
+
+@testset "Input map validation" begin
+    import ModelingToolkit: InvalidKeyError, MissingParametersError 
+    @variables X(t)
+    @parameters p d
+    eqs = [D(X) ~ p - d*X]
+    @mtkbuild osys = ODESystem(eqs, t)
+    
+    p = "I accidentally renamed p"
+    u0 = [X => 1.0]
+    ps = [p => 1.0, d => 0.5]
+    @test_throws MissingParametersError oprob = ODEProblem(osys, u0, (0.0, 1.0), ps)
+    
+    @parameters p d
+    ps = [p => 1.0, d => 0.5, "Random stuff" => 3.0]
+    @test_throws InvalidKeyError oprob = ODEProblem(osys, u0, (0.0, 1.0), ps)
+
+    u0 = [:X => 1.0, "random" => 3.0]
+    @test_throws InvalidKeyError oprob = ODEProblem(osys, u0, (0.0, 1.0), ps)
+
+    @variables x(t) y(t) z(t)
+    @parameters a b c d 
+    eqs = [D(x) ~ x*a, D(y) ~ y*c, D(z) ~ b + d]
+    @mtkbuild sys = ODESystem(eqs, t)
+    pmap = [a => 1, b => 2, c => 3, d => 4, "b" => 2]
+    u0map = [x => 1, y => 2, z => 3]
+    @test_throws InvalidKeyError ODEProblem(sys, u0map, (0., 1.), pmap)
+
+    pmap = [a => 1, b => 2, c => 3, d => 4]
+    u0map = [x => 1, y => 2, z => 3, :0 => 3]
+    @test_throws InvalidKeyError ODEProblem(sys, u0map, (0., 1.), pmap)
+end