diff --git a/pkg/ctl/cmdutils/configfile_test.go b/pkg/ctl/cmdutils/configfile_test.go
index d5185374a6..42964d7cba 100644
--- a/pkg/ctl/cmdutils/configfile_test.go
+++ b/pkg/ctl/cmdutils/configfile_test.go
@@ -140,7 +140,7 @@ var _ = Describe("cmdutils configfile", func() {
 					l.flagsIncompatibleWithConfigFile.Delete("name")
 
 					err := l.Load()
-					Expect(err).To(MatchError(ContainSubstring("error unmarshaling JSON: while decoding JSON: json: unknown field \"containerRuntime\"")))
+					Expect(err).To(MatchError(ContainSubstring("strict decoding error: unknown field \"managedNodeGroups[0].containerRuntime\"")))
 				})
 			})
 		})
diff --git a/pkg/eks/api.go b/pkg/eks/api.go
index 5e36056bce..e1bf87a95d 100644
--- a/pkg/eks/api.go
+++ b/pkg/eks/api.go
@@ -21,9 +21,9 @@ import (
 	"github.com/aws/aws-sdk-go-v2/service/sts"
 	"github.com/kris-nova/logger"
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/runtime/serializer"
 	k8sclient "k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/kubernetes/scheme"
-	"sigs.k8s.io/yaml"
 
 	"github.com/weaveworks/eksctl/pkg/ami"
 	api "github.com/weaveworks/eksctl/pkg/apis/eksctl.io/v1alpha5"
@@ -217,18 +217,12 @@ func newAWSProvider(spec *api.ProviderConfig, configurationLoader AWSConfigurati
 	return provider, nil
 }
 
+// The default deserializer silently drops unknown and mis-cased keys.
+var strictDeserializer = serializer.NewCodecFactory(scheme.Scheme, serializer.EnableStrict).UniversalDeserializer()
+
 // ParseConfig parses data into a ClusterConfig
 func ParseConfig(data []byte) (*api.ClusterConfig, error) {
-	// strict mode is not available in runtime.Decode, so we use the parser
-	// directly; we don't store the resulting object, this is just the means
-	// of detecting any unknown keys
-	// NOTE: we must use sigs.k8s.io/yaml, as it behaves differently from
-	// github.com/ghodss/yaml, which didn't handle nested structs well
-	if err := yaml.UnmarshalStrict(data, &api.ClusterConfig{}); err != nil {
-		return nil, err
-	}
-
-	obj, err := runtime.Decode(scheme.Codecs.UniversalDeserializer(), data)
+	obj, err := runtime.Decode(strictDeserializer, data)
 	if err != nil {
 		return nil, err
 	}
diff --git a/pkg/eks/api_test.go b/pkg/eks/api_test.go
index 5d31b0f3e5..3d89570d12 100644
--- a/pkg/eks/api_test.go
+++ b/pkg/eks/api_test.go
@@ -215,19 +215,44 @@ var _ = Describe("eksctl API", func() {
 		It("should reject unknown field in a YAML config", func() {
 			_, err := eks.LoadConfigFromFile("testdata/bad-field-1.yaml")
 			Expect(err).To(HaveOccurred())
-			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-1.yaml": error unmarshaling JSON: while decoding JSON: json: unknown field "zone"`))
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-1.yaml": strict decoding error: unknown field "metadata.zone"`))
 		})
 
 		It("should reject unknown field in a YAML config", func() {
 			_, err := eks.LoadConfigFromFile("testdata/bad-field-2.yaml")
 			Expect(err).To(HaveOccurred())
-			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-2.yaml": error unmarshaling JSON: while decoding JSON: json: unknown field "bar"`))
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-2.yaml": strict decoding error: unknown field "nodeGroups[0].iam.withAddonPolicies.bar"`))
 		})
 
 		It("should reject unknown field in a JSON config", func() {
 			_, err := eks.LoadConfigFromFile("testdata/bad-field-1.json")
 			Expect(err).To(HaveOccurred())
-			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-1.json": error unmarshaling JSON: while decoding JSON: json: unknown field "nodes"`))
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-1.json": strict decoding error: unknown field "nodeGroups[0].nodes"`))
+		})
+
+		It("should reject a duplicate key in a YAML config", func() {
+			_, err := eks.LoadConfigFromFile("testdata/duplicate-key-1.yaml")
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/duplicate-key-1.yaml": strict decoding error: yaml: unmarshal errors:`))
+			Expect(err.Error()).To(ContainSubstring(`key "name" already set in map`))
+		})
+
+		It("should report a type error before unknown fields", func() {
+			_, err := eks.LoadConfigFromFile("testdata/bad-type-2.yaml")
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-type-2.yaml": json: cannot unmarshal bool into Go struct field`))
+		})
+
+		It("should reject a top-level field with the wrong case", func() {
+			_, err := eks.LoadConfigFromFile("testdata/bad-field-case-1.yaml")
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-case-1.yaml": strict decoding error: unknown field "NodeGroups"`))
+		})
+
+		It("should reject a nested field with the wrong case", func() {
+			_, err := eks.LoadConfigFromFile("testdata/bad-field-case-2.yaml")
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(HavePrefix(`loading config file "testdata/bad-field-case-2.yaml": strict decoding error: unknown field "managedNodeGroups[0].capacityReservation.capacityReservationTarget.capacityReservationId"`))
 		})
 
 		It("should reject old API version", func() {
diff --git a/pkg/eks/testdata/bad-field-1.json b/pkg/eks/testdata/bad-field-1.json
index d717554e6b..c2882eb0dc 100644
--- a/pkg/eks/testdata/bad-field-1.json
+++ b/pkg/eks/testdata/bad-field-1.json
@@ -1,5 +1,5 @@
 {
-  "apiVersion": "eksctl.io/v1alpha3",
+  "apiVersion": "eksctl.io/v1alpha5",
   "kind": "ClusterConfig",
   "metadata": {
     "name": "cluster-1",
diff --git a/pkg/eks/testdata/bad-field-2.yaml b/pkg/eks/testdata/bad-field-2.yaml
index 7f1279147a..7641fe8e8e 100644
--- a/pkg/eks/testdata/bad-field-2.yaml
+++ b/pkg/eks/testdata/bad-field-2.yaml
@@ -10,7 +10,8 @@ nodeGroups:
   - name: ng-1
     instanceType: m5.large
     desiredCapacity: 10
-    ssh: true
+    ssh:
+      allow: true
     iam:
       withAddonPolicies:
          foo: 1
diff --git a/pkg/eks/testdata/bad-field-case-1.yaml b/pkg/eks/testdata/bad-field-case-1.yaml
new file mode 100644
index 0000000000..3b66b88d13
--- /dev/null
+++ b/pkg/eks/testdata/bad-field-case-1.yaml
@@ -0,0 +1,11 @@
+---
+apiVersion: eksctl.io/v1alpha5
+kind: ClusterConfig
+
+metadata:
+  name: cluster-1
+  region: eu-north-1
+
+NodeGroups:
+  - name: ng-1
+    instanceType: m5.large
diff --git a/pkg/eks/testdata/bad-field-case-2.yaml b/pkg/eks/testdata/bad-field-case-2.yaml
new file mode 100644
index 0000000000..19bdd7433c
--- /dev/null
+++ b/pkg/eks/testdata/bad-field-case-2.yaml
@@ -0,0 +1,13 @@
+---
+apiVersion: eksctl.io/v1alpha5
+kind: ClusterConfig
+
+metadata:
+  name: cluster-1
+  region: eu-north-1
+
+managedNodeGroups:
+  - name: mng-1
+    capacityReservation:
+      capacityReservationTarget:
+        capacityReservationId: cr-0123456789abcdef0
diff --git a/pkg/eks/testdata/bad-type-2.yaml b/pkg/eks/testdata/bad-type-2.yaml
new file mode 100644
index 0000000000..773dafe7a3
--- /dev/null
+++ b/pkg/eks/testdata/bad-type-2.yaml
@@ -0,0 +1,14 @@
+---
+apiVersion: eksctl.io/v1alpha5
+kind: ClusterConfig
+
+metadata:
+  name: cluster-1
+  region: eu-north-1
+
+nodeGroups:
+  - name: ng-1
+    ssh: true
+    iam:
+      withAddonPolicies:
+        foo: 1
diff --git a/pkg/eks/testdata/duplicate-key-1.yaml b/pkg/eks/testdata/duplicate-key-1.yaml
new file mode 100644
index 0000000000..6237d7ec1d
--- /dev/null
+++ b/pkg/eks/testdata/duplicate-key-1.yaml
@@ -0,0 +1,8 @@
+---
+apiVersion: eksctl.io/v1alpha5
+kind: ClusterConfig
+
+metadata:
+  name: cluster-1
+  name: cluster-2
+  region: eu-north-1