diff --git a/lib/ControlSystemsBase/src/types/SisoTfTypes/SisoZpk.jl b/lib/ControlSystemsBase/src/types/SisoTfTypes/SisoZpk.jl
index 91ec7d191..9e3f87f54 100644
--- a/lib/ControlSystemsBase/src/types/SisoTfTypes/SisoZpk.jl
+++ b/lib/ControlSystemsBase/src/types/SisoTfTypes/SisoZpk.jl
@@ -79,11 +79,12 @@ function minreal(sys::SisoZpk{T,TR}, eps::Real) where {T, TR}
             distance, zidx = findmin(abs.(p .- newZ))
 
             if distance < eps
-                if imag(p) == 0 && imag(newZ[zidx]) != 0
+                if imag(p) == 0 && imag(newZ[zidx]) != 0 && zidx < length(newZ)
                     newZ[zidx+1] = real(newZ[zidx+1])
                 end
                 if imag(newZ[zidx]) == 0 && imag(p) != 0
                     pidx += 1
+                    pidx > length(sys.p) && (deleteat!(newZ, zidx); break)
                     p = real(sys.p[pidx])
                     deleteat!(newZ, zidx)
                     continue
diff --git a/lib/ControlSystemsBase/test/test_zpk.jl b/lib/ControlSystemsBase/test/test_zpk.jl
index 955eb5cbc..94fb10ea7 100644
--- a/lib/ControlSystemsBase/test/test_zpk.jl
+++ b/lib/ControlSystemsBase/test/test_zpk.jl
@@ -144,6 +144,14 @@ k = 0.3
 @test minreal(zpk([-1.0, -2.0], Float64[], 2.5)) == zpk([-1.0, -2.0], Float64[], 2.5)
 @test minreal(zpk(Float64[], [-1.0, -2.0], 2.5)) == zpk(Float64[], [-1.0, -2.0], 2.5)
 
+# Regression: bounds-checks in SisoZpk minreal. With complex-valued zpk the
+# constructor does not enforce conjugate-pair ordering, so the cancellation
+# loop can hit `newZ[zidx+1]` (line 83) with `zidx == length(newZ)`, or
+# advance `pidx` past `length(sys.p)` before reading `sys.p[pidx]` (line 87).
+# Both previously threw BoundsError; they should now return cleanly.
+@test minreal(zpk([1.0+0.001im, 1.0-0.001im], [1.0, 1.0+0.001im], 1.0+0im), 0.01) == zpk(ComplexF64[], ComplexF64[], 1.0+0im)
+@test minreal(zpk([1.0+0.001im, 1.0-0.001im], [1.0+0.001im, 1.0], 1.0+0im), 0.01) == zpk(ComplexF64[], ComplexF64[], 1.0+0im)
+
 # Test type inference
 @test eltype(fill(zpk("s"),2)) <: TransferFunction
 @test eltype(fill(zpk([1],[1,1],1),2)) <: TransferFunction