diff --git a/lib/resty/openapi_validator/params.lua b/lib/resty/openapi_validator/params.lua
index 6ca39dc..36d6634 100644
--- a/lib/resty/openapi_validator/params.lua
+++ b/lib/resty/openapi_validator/params.lua
@@ -453,7 +453,12 @@ function _M.validate(route, path_params, query_args, headers, skip)
     end
 
     if not skip.header and route.params.header then
-        validate_param_group(route.params.header, "header", headers)
+        -- Normalize header keys to lowercase for case-insensitive matching
+        local lower_headers = {}
+        for k, v in pairs(headers) do
+            lower_headers[str_lower(k)] = v
+        end
+        validate_param_group(route.params.header, "header", lower_headers)
     end
 
     if #errs > 0 then
diff --git a/t/conformance/test_validate_header.lua b/t/conformance/test_validate_header.lua
index 00596f5..bbb37d7 100644
--- a/t/conformance/test_validate_header.lua
+++ b/t/conformance/test_validate_header.lua
@@ -46,7 +46,33 @@ T.describe("header: missing required headers", function()
     T.like(err, "[Cc]ontent%-[Tt]ype", "error mentions Content-Type")
 end)
 
--- TEST 3: skip header validation
+-- TEST 3: case-insensitive header matching (spec has capitalized names, request uses exact match)
+T.describe("header: case-insensitive match with exact case keys", function()
+    local ok, err = validator:validate_request({
+        method = "GET",
+        path = "/validateHeaders",
+        headers = {
+            ["Authorization"] = "Bearer dGVzdA==.dGVzdA==.dGVzdA==",
+            ["Content-Type"] = "application/json",
+        },
+    })
+    T.ok(ok, "exact case headers pass: " .. tostring(err))
+end)
+
+-- TEST 4: case-insensitive header matching (spec has capitalized names, request all uppercase)
+T.describe("header: case-insensitive match with uppercase keys", function()
+    local ok, err = validator:validate_request({
+        method = "GET",
+        path = "/validateHeaders",
+        headers = {
+            ["AUTHORIZATION"] = "Bearer dGVzdA==.dGVzdA==.dGVzdA==",
+            ["CONTENT-TYPE"] = "application/json",
+        },
+    })
+    T.ok(ok, "uppercase headers pass: " .. tostring(err))
+end)
+
+-- TEST 5: skip header validation
 T.describe("header: skip header validation", function()
     local ok, err = validator:validate_request({
         method = "GET",
diff --git a/t/unit/test_params.lua b/t/unit/test_params.lua
index 9d5aa59..35646f4 100644
--- a/t/unit/test_params.lua
+++ b/t/unit/test_params.lua
@@ -315,4 +315,42 @@ T.describe("params: deepObject anyOf composed (allOf) object branch", function()
     T.ok(not errs or #errs == 0, "no errors")
 end)
 
+-- Header case-insensitive matching: spec has lowercase name, request has
+-- canonical case key (e.g. HTTP/1.1 clients sending X-Client-Id).
+T.describe("params: header case-insensitive match (canonical case)", function()
+    local route = make_route({
+        { name = "x-client-id", ["in"] = "header", required = true,
+          schema = { type = "string" } },
+    }, "header")
+
+    local ok, errs = params_mod.validate(route, {}, {},
+        { ["X-Client-Id"] = "test123" })
+    T.ok(ok, "canonical case header found")
+    T.ok(not errs or #errs == 0, "no errors")
+end)
+
+T.describe("params: header case-insensitive match (uppercase)", function()
+    local route = make_route({
+        { name = "x-client-id", ["in"] = "header", required = true,
+          schema = { type = "string" } },
+    }, "header")
+
+    local ok, errs = params_mod.validate(route, {}, {},
+        { ["X-CLIENT-ID"] = "test123" })
+    T.ok(ok, "uppercase header found")
+    T.ok(not errs or #errs == 0, "no errors")
+end)
+
+T.describe("params: header case-insensitive match (spec has mixed case)", function()
+    local route = make_route({
+        { name = "Authorization", ["in"] = "header", required = true,
+          schema = { type = "string" } },
+    }, "header")
+
+    local ok, errs = params_mod.validate(route, {}, {},
+        { ["authorization"] = "Bearer token" })
+    T.ok(ok, "lowercase header matches mixed-case spec name")
+    T.ok(not errs or #errs == 0, "no errors")
+end)
+
 T.done()