diff --git a/lib/postgrex/extensions/interval.ex b/lib/postgrex/extensions/interval.ex
index 7860eb70..5fa91b2e 100644
--- a/lib/postgrex/extensions/interval.ex
+++ b/lib/postgrex/extensions/interval.ex
@@ -3,7 +3,16 @@ defmodule Postgrex.Extensions.Interval do
   import Postgrex.BinaryUtils, warn: false
   use Postgrex.BinaryExtension, send: "interval_send"
 
-  def init(opts), do: Keyword.get(opts, :interval_decode_type, Postgrex.Interval)
+  def init(opts) do
+    case Keyword.get(opts, :interval_decode_type, Postgrex.Interval) do
+      type when type in [Postgrex.Interval, Duration] ->
+        type
+
+      other ->
+        raise ArgumentError,
+              "#{inspect(other)} is not valid for `:interval_decode_type`. Please use either `Postgrex.Interval` or `Duration`"
+    end
+  end
 
   if Code.ensure_loaded?(Duration) do
     import Bitwise, warn: false
@@ -43,48 +52,60 @@ defmodule Postgrex.Extensions.Interval do
     def decode(type) do
       quote location: :keep do
         <<16::int32(), microseconds::int64(), days::int32(), months::int32()>> ->
-          seconds = div(microseconds, 1_000_000)
-          microseconds = rem(microseconds, 1_000_000)
-
-          case unquote(type) do
-            Postgrex.Interval ->
-              %Postgrex.Interval{
-                months: months,
-                days: days,
-                secs: seconds,
-                microsecs: microseconds
-              }
-
-            Duration ->
-              years = div(months, 12)
-              months = rem(months, 12)
-              weeks = div(days, 7)
-              days = rem(days, 7)
-              minutes = div(seconds, 60)
-              seconds = rem(seconds, 60)
-              hours = div(minutes, 60)
-              minutes = rem(minutes, 60)
-              type_mod = var!(mod)
-              precision = if type_mod, do: type_mod &&& unquote(@precision_mask)
-
-              precision =
-                if precision in unquote(@unspecified_precision),
-                  do: unquote(@default_precision),
-                  else: precision
-
-              Duration.new!(
-                year: years,
-                month: months,
-                week: weeks,
-                day: days,
-                hour: hours,
-                minute: minutes,
-                second: seconds,
-                microsecond: {microseconds, precision}
-              )
-          end
+          precision = if var!(mod), do: var!(mod) &&& unquote(@precision_mask)
+
+          unquote(__MODULE__).decode_interval(
+            microseconds,
+            days,
+            months,
+            precision,
+            unquote(type)
+          )
       end
     end
+
+    ## Helpers
+
+    def decode_interval(microseconds, days, months, _precision, Postgrex.Interval) do
+      seconds = div(microseconds, 1_000_000)
+      microseconds = rem(microseconds, 1_000_000)
+
+      %Postgrex.Interval{
+        months: months,
+        days: days,
+        secs: seconds,
+        microsecs: microseconds
+      }
+    end
+
+    def decode_interval(microseconds, days, months, precision, Duration) do
+      years = div(months, 12)
+      months = rem(months, 12)
+      weeks = div(days, 7)
+      days = rem(days, 7)
+      seconds = div(microseconds, 1_000_000)
+      microseconds = rem(microseconds, 1_000_000)
+      minutes = div(seconds, 60)
+      seconds = rem(seconds, 60)
+      hours = div(minutes, 60)
+      minutes = rem(minutes, 60)
+
+      precision =
+        if precision in unquote(@unspecified_precision),
+          do: unquote(@default_precision),
+          else: precision
+
+      Duration.new!(
+        year: years,
+        month: months,
+        week: weeks,
+        day: days,
+        hour: hours,
+        minute: minutes,
+        second: seconds,
+        microsecond: {microseconds, precision}
+      )
+    end
   else
     def encode(_) do
       quote location: :keep do
@@ -100,10 +121,22 @@ defmodule Postgrex.Extensions.Interval do
     def decode(_) do
       quote location: :keep do
         <<16::int32(), microseconds::int64(), days::int32(), months::int32()>> ->
-          seconds = div(microseconds, 1_000_000)
-          microseconds = rem(microseconds, 1_000_000)
-          %Postgrex.Interval{months: months, days: days, secs: seconds, microsecs: microseconds}
+          unquote(__MODULE__).decode_interval(microseconds, days, months, nil, Postgrex.Interval)
       end
     end
+
+    ## Helpers
+
+    def decode_interval(microseconds, days, months, _precision, Postgrex.Interval) do
+      seconds = div(microseconds, 1_000_000)
+      microseconds = rem(microseconds, 1_000_000)
+
+      %Postgrex.Interval{
+        months: months,
+        days: days,
+        secs: seconds,
+        microsecs: microseconds
+      }
+    end
   end
 end