diff --git a/src/systems/diffeqs/odesystem.jl b/src/systems/diffeqs/odesystem.jl
index 61f16fd926..b31f39ec22 100644
--- a/src/systems/diffeqs/odesystem.jl
+++ b/src/systems/diffeqs/odesystem.jl
@@ -202,6 +202,7 @@ struct ODESystem <: AbstractODESystem
             check_parameters(ps, iv)
             check_equations(deqs, iv)
             check_equations(equations(cevents), iv)
+            check_var_types(ODESystem, dvs)
         end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(dvs, ps, iv)
diff --git a/src/systems/diffeqs/sdesystem.jl b/src/systems/diffeqs/sdesystem.jl
index 366e8a6d09..eeedce1d46 100644
--- a/src/systems/diffeqs/sdesystem.jl
+++ b/src/systems/diffeqs/sdesystem.jl
@@ -170,6 +170,7 @@ struct SDESystem <: AbstractODESystem
             check_parameters(ps, iv)
             check_equations(deqs, iv)
             check_equations(neqs, dvs)
+            check_var_types(SDESystem, dvs)
             if size(neqs, 1) != length(deqs)
                 throw(ArgumentError("Noise equations ill-formed. Number of rows must match number of drift equations. size(neqs,1) = $(size(neqs,1)) != length(deqs) = $(length(deqs))"))
             end
diff --git a/src/systems/discrete_system/discrete_system.jl b/src/systems/discrete_system/discrete_system.jl
index bd5c72eec7..fb6dfe0236 100644
--- a/src/systems/discrete_system/discrete_system.jl
+++ b/src/systems/discrete_system/discrete_system.jl
@@ -122,6 +122,7 @@ struct DiscreteSystem <: AbstractTimeDependentSystem
             check_independent_variables([iv])
             check_variables(dvs, iv)
             check_parameters(ps, iv)
+            check_var_types(DiscreteSystem, dvs)
         end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(dvs, ps, iv)
diff --git a/src/systems/jumps/jumpsystem.jl b/src/systems/jumps/jumpsystem.jl
index 5c0a61771a..e5dbb185e2 100644
--- a/src/systems/jumps/jumpsystem.jl
+++ b/src/systems/jumps/jumpsystem.jl
@@ -147,6 +147,7 @@ struct JumpSystem{U <: ArrayPartition} <: AbstractTimeDependentSystem
             check_independent_variables([iv])
             check_variables(unknowns, iv)
             check_parameters(ps, iv)
+            check_var_types(JumpSystem, unknowns)
         end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(unknowns, ps, iv)
diff --git a/src/systems/nonlinear/nonlinearsystem.jl b/src/systems/nonlinear/nonlinearsystem.jl
index 6b0b0cc759..687d55b9bb 100644
--- a/src/systems/nonlinear/nonlinearsystem.jl
+++ b/src/systems/nonlinear/nonlinearsystem.jl
@@ -115,6 +115,9 @@ struct NonlinearSystem <: AbstractTimeIndependentSystem
             tearing_state = nothing, substitutions = nothing,
             complete = false, index_cache = nothing, parent = nothing,
             isscheduled = false; checks::Union{Bool, Int} = true)
+        if checks == true || (checks & CheckComponents) > 0
+            check_var_types(NonlinearSystem, unknowns)
+        end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(unknowns, ps)
             check_units(u, eqs)
diff --git a/src/systems/optimization/optimizationsystem.jl b/src/systems/optimization/optimizationsystem.jl
index 860e063e35..de4696bfa2 100644
--- a/src/systems/optimization/optimizationsystem.jl
+++ b/src/systems/optimization/optimizationsystem.jl
@@ -73,6 +73,9 @@ struct OptimizationSystem <: AbstractOptimizationSystem
             gui_metadata = nothing, complete = false, index_cache = nothing, parent = nothing,
             isscheduled = false;
             checks::Union{Bool, Int} = true)
+        if checks == true || (checks & CheckComponents) > 0
+            check_var_types(OptimizationSystem, unknowns)
+        end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(unknowns, ps)
             unwrap(op) isa Symbolic && check_units(u, op)
diff --git a/src/systems/pde/pdesystem.jl b/src/systems/pde/pdesystem.jl
index eac540e401..e067f0e149 100644
--- a/src/systems/pde/pdesystem.jl
+++ b/src/systems/pde/pdesystem.jl
@@ -102,6 +102,9 @@ struct PDESystem <: ModelingToolkit.AbstractMultivariateSystem
             checks::Union{Bool, Int} = true,
             description = "",
             name)
+        if checks == true || (checks & CheckComponents) > 0
+            check_var_types(PDESystem, dvs)
+        end
         if checks == true || (checks & CheckUnits) > 0
             u = __get_unit_type(dvs, ivs, ps)
             check_units(u, eqs)
diff --git a/src/utils.jl b/src/utils.jl
index 5e4f0b52d2..736a4cc03e 100644
--- a/src/utils.jl
+++ b/src/utils.jl
@@ -155,6 +155,17 @@ function check_variables(dvs, iv)
     end
 end
 
+function check_var_types(sys_type::Type{T}, dvs) where T <: AbstractSystem
+    if any(u -> !(symtype(u) <: Number || eltype(symtype(u)) <: Number), dvs)
+        error("The type of unknown variables must be a numeric type.")
+    elseif any(u -> (symtype(u) !== symtype(dvs[1])), dvs)
+        error("The type of all the unknown variables in a system must all be the same.")
+    elseif sys_type == ODESystem || sys_type == SDESystem || sys_type == PDESystem
+        any(u -> !(symtype(u) == Real || eltype(symtype(u)) == Real), dvs) && error("The type of unknown variables for an SDESystem, PDESystem, or ODESystem should not be a concrete numeric type.")
+    end
+    nothing
+end
+
 function check_lhs(eq::Equation, op, dvs::Set)
     v = unwrap(eq.lhs)
     _iszero(v) && return
@@ -1182,3 +1193,4 @@ function guesses_from_metadata!(guesses, vars)
         guesses[vars[i]] = varguesses[i]
     end
 end
+
diff --git a/test/odesystem.jl b/test/odesystem.jl
index 76c47a8f1d..b31b58002a 100644
--- a/test/odesystem.jl
+++ b/test/odesystem.jl
@@ -1553,6 +1553,13 @@ end
     @test all(x -> any(isapprox(x, atol = 1e-6), sol2.t), expected_tstops)
 end
 
+@testset "Validate input types" begin
+    @parameters p d
+    @variables X(t)::Int64
+    eq = D(X) ~ p - d*X
+    @test_throws Exception @mtkbuild osys = ODESystem([eq], t)
+end
+
 @testset "dae_order_lowering basic test" begin
     @parameters a
     @variables x(t) y(t) z(t)
@@ -1608,4 +1615,4 @@ end
 
     prob = ODEProblem{false}(lowered_dae_sys; u0_constructor = x -> SVector(x...))
     @test prob.u0 isa SVector
-end
\ No newline at end of file
+end
diff --git a/test/sdesystem.jl b/test/sdesystem.jl
index 8069581dcc..f638eaed9d 100644
--- a/test/sdesystem.jl
+++ b/test/sdesystem.jl
@@ -868,3 +868,12 @@ end
     @test length(ModelingToolkit.get_noiseeqs(sys)) == 1
     @test length(observed(sys)) == 1
 end
+
+# Test validating types of states
+@testset "Validate input types" begin
+    @parameters p d
+    @variables X(t)::Int64
+    @brownian z
+    eq2 = D(X) ~ p - d*X + z
+    @test_throws Exception @mtkbuild ssys = System([eq2], t)
+end