diff --git a/CHANGELOG.md b/CHANGELOG.md
index b623030..f9f7ca7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - "error" type supported.
 - "datetime" type supported.
+- "interval" type supported.
 
 ### Fixed
 
diff --git a/checks.lua b/checks.lua
index 649de38..3154a8e 100644
--- a/checks.lua
+++ b/checks.lua
@@ -354,4 +354,6 @@ if has_datetime then
     checkers.datetime = datetime.is_datetime
 end
 
+add_ffi_type_checker('interval', 'struct interval')
+
 return checks
diff --git a/test.lua b/test.lua
index c359006..151278f 100755
--- a/test.lua
+++ b/test.lua
@@ -633,6 +633,12 @@ if has_datetime then
     testdata.datetime = datetime
 end
 
+function testdata.fn_interval(arg) -- luacheck: no unused args
+    checks('interval')
+end
+
+local has_interval = has_datetime and datetime.interval ~= nil
+
 local ret_cases = {
     -- fn_int64
     {
@@ -1037,6 +1043,36 @@ local ret_cases = {
         code = 'fn_datetime({year=2023, month=1, day=11})',
         ok = false,
     },
+
+    -- fn_interval
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new())',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new{day=1})',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval(datetime.interval.new{month=1, adjust="last"})',
+        ok = true,
+        additional_data = {'datetime'},
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval()',
+        ok = false,
+    },
+    {
+        skip = not has_interval,
+        code = 'fn_interval({month=1, adjust="last"})',
+        ok = false,
+    },
 }
 
 for _, case in pairs(ret_cases) do