diff --git a/Project.toml b/Project.toml
index 2d1ad771..2f7a3ab1 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "DataInterpolations"
 uuid = "82cc6244-b520-54b8-b5a6-8a565e85f1d0"
-version = "4.4.0"
+version = "4.4.1"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
diff --git a/src/derivatives.jl b/src/derivatives.jl
index 85aa5264..73fd0b86 100644
--- a/src/derivatives.jl
+++ b/src/derivatives.jl
@@ -1,5 +1,5 @@
 function derivative(A, t)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     derivative(A, t, firstindex(A.t) - 1)[1]
 end
 
@@ -36,7 +36,7 @@ function derivative(A::QuadraticInterpolation{<:AbstractMatrix}, t::Number, igue
 end
 
 function derivative(A::LagrangeInterpolation{<:AbstractVector}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     idxs = findRequiredIdxs(A, t)
     if A.t[idxs[1]] == t
         return zero(A.u[idxs[1]])
@@ -72,7 +72,7 @@ function derivative(A::LagrangeInterpolation{<:AbstractVector}, t::Number)
 end
 
 function derivative(A::LagrangeInterpolation{<:AbstractMatrix}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     idxs = findRequiredIdxs(A, t)
     if A.t[idxs[1]] == t
         return zero(A.u[:, idxs[1]])
@@ -120,12 +120,12 @@ function derivative(A::AkimaInterpolation{<:AbstractVector}, t::Number, iguess)
 end
 
 function derivative(A::ConstantInterpolation{<:AbstractVector}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     return isempty(searchsorted(A.t, t)) ? zero(A.u[1]) : eltype(A.u)(NaN)
 end
 
 function derivative(A::ConstantInterpolation{<:AbstractMatrix}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     return isempty(searchsorted(A.t, t)) ? zero(A.u[:, 1]) : eltype(A.u)(NaN) .* A.u[:, 1]
 end
 
diff --git a/src/interpolation_methods.jl b/src/interpolation_methods.jl
index 8b781a8e..9b1ff806 100644
--- a/src/interpolation_methods.jl
+++ b/src/interpolation_methods.jl
@@ -1,5 +1,5 @@
 function _interpolate(interp, t)
-    ((t < interp.t[1] || t > interp.t[end]) && !interp.extrapolate) &&
+    ((t <= interp.t[1] || t >= interp.t[end]) && !interp.extrapolate) &&
         throw(ExtrapolationError())
     _interpolate(interp, t, firstindex(interp.t) - 1)[1]
 end
@@ -57,7 +57,7 @@ end
 
 # Lagrange Interpolation
 function _interpolate(A::LagrangeInterpolation{<:AbstractVector}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     idxs = findRequiredIdxs(A, t)
     if A.t[idxs[1]] == t
         return A.u[idxs[1]]
@@ -86,7 +86,7 @@ function _interpolate(A::LagrangeInterpolation{<:AbstractVector}, t::Number)
 end
 
 function _interpolate(A::LagrangeInterpolation{<:AbstractMatrix}, t::Number)
-    ((t < A.t[1] || t > A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
+    ((t <= A.t[1] || t >= A.t[end]) && !A.extrapolate) && throw(ExtrapolationError())
     idxs = findRequiredIdxs(A, t)
     if A.t[idxs[1]] == t
         return A.u[:, idxs[1]]