diff --git a/aead/aesgcm/key.go b/aead/aesgcm/key.go
index 8edeebc..5e29709 100644
--- a/aead/aesgcm/key.go
+++ b/aead/aesgcm/key.go
@@ -101,19 +101,26 @@ type ParametersOpts struct {
 	Variant        Variant
 }
 
-// NewParameters creates a new AES-GCM Parameters object.
-func NewParameters(opts ParametersOpts) (*Parameters, error) {
+func validateOpts(opts *ParametersOpts) error {
 	if opts.KeySizeInBytes != 16 && opts.KeySizeInBytes != 24 && opts.KeySizeInBytes != 32 {
-		return nil, fmt.Errorf("aesgcm.Parameters: unsupported key size; want 16, 24, or 32, got: %v", opts.KeySizeInBytes)
+		return fmt.Errorf("unsupported key size; want 16, 24, or 32, got: %v", opts.KeySizeInBytes)
 	}
 	if opts.IVSizeInBytes <= 0 {
-		return nil, fmt.Errorf("aesgcm.Parameters: unsupported IV size; want > 0, got: %v", opts.IVSizeInBytes)
+		return fmt.Errorf("unsupported IV size; want > 0, got: %v", opts.IVSizeInBytes)
 	}
 	if opts.TagSizeInBytes < 12 || opts.TagSizeInBytes > 16 {
-		return nil, fmt.Errorf("aesgcm.Parameters: unsupported tag size; want >= 12 and <= 16, got: %v", opts.TagSizeInBytes)
+		return fmt.Errorf("unsupported tag size; want >= 12 and <= 16, got: %v", opts.TagSizeInBytes)
 	}
 	if opts.Variant == VariantUnknown {
-		return nil, fmt.Errorf("aesgcm.Parameters: unsupported variant: %v", opts.Variant)
+		return fmt.Errorf("unsupported variant: %v", opts.Variant)
+	}
+	return nil
+}
+
+// NewParameters creates a new AES-GCM Parameters object.
+func NewParameters(opts ParametersOpts) (*Parameters, error) {
+	if err := validateOpts(&opts); err != nil {
+		return nil, fmt.Errorf("aesgcm.NewParameters: %v", err)
 	}
 	return &Parameters{
 		keySizeInBytes: opts.KeySizeInBytes,
@@ -151,6 +158,17 @@ func NewKey(keyBytes secretdata.Bytes, keyID uint32, parameters *Parameters) (*K
 	if parameters == nil {
 		return nil, fmt.Errorf("aesgcm.NewKey: parameters is nil")
 	}
+
+	opts := &ParametersOpts{
+		KeySizeInBytes: parameters.KeySizeInBytes(),
+		IVSizeInBytes:  parameters.IVSizeInBytes(),
+		TagSizeInBytes: parameters.TagSizeInBytes(),
+		Variant:        parameters.Variant(),
+	}
+	if err := validateOpts(opts); err != nil {
+		return nil, fmt.Errorf("aesgcm.NewKey: %v", err)
+	}
+
 	if keyBytes.Len() != int(parameters.KeySizeInBytes()) {
 		return nil, fmt.Errorf("aesgcm.NewKey: key.Len() = %v, want %v", keyBytes.Len(), parameters.KeySizeInBytes())
 	}
diff --git a/aead/aesgcm/key_test.go b/aead/aesgcm/key_test.go
index 809522a..bdae1c9 100644
--- a/aead/aesgcm/key_test.go
+++ b/aead/aesgcm/key_test.go
@@ -91,6 +91,70 @@ func TestNewParametersInvalidVariant(t *testing.T) {
 	}
 }
 
+func TestNewKeyFailsIfParametersIsNil(t *testing.T) {
+	keyBytes, err := secretdata.NewBytesFromRand(32)
+	if err != nil {
+		t.Fatalf("secretdata.NewBytesFromRand(32) err = %v, want nil", err)
+	}
+	if _, err := aesgcm.NewKey(*keyBytes, 123, nil); err == nil {
+		t.Errorf("aesgcm.NewKey(*keyBytes, 123, nil) err = nil, want error")
+	}
+}
+
+func TestNewKeyFailsIfKeySizeIsDifferentThanParameters(t *testing.T) {
+	for _, tc := range []struct {
+		name     string
+		keyBytes *secretdata.Bytes
+		params   aesgcm.ParametersOpts
+	}{
+		{
+			name:     "key size is 16 but parameters is 32",
+			keyBytes: secretdata.NewBytesFromData(key128Bits, insecuresecretdataaccess.Token{}),
+			params: aesgcm.ParametersOpts{
+				KeySizeInBytes: 32,
+				IVSizeInBytes:  12,
+				TagSizeInBytes: 16,
+				Variant:        aesgcm.VariantTink,
+			},
+		},
+		{
+			name:     "key size is 32 but parameters is 16",
+			keyBytes: secretdata.NewBytesFromData(key256Bits, insecuresecretdataaccess.Token{}),
+			params: aesgcm.ParametersOpts{
+				KeySizeInBytes: 16,
+				IVSizeInBytes:  12,
+				TagSizeInBytes: 16,
+				Variant:        aesgcm.VariantTink,
+			},
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			params, err := aesgcm.NewParameters(tc.params)
+			if err != nil {
+				t.Fatalf("aesgcm.NewParameters(%v) err = %v, want nil", tc.params, err)
+			}
+			if _, err := aesgcm.NewKey(*tc.keyBytes, 123, params); err == nil {
+				t.Errorf("aesgcm.NewKey(%v, 123, %v) err = nil, want error", tc.keyBytes, params)
+			}
+		})
+	}
+}
+
+// TestNewKeyFailsIfInvalidParams tests that NewKey fails if the parameters are invalid.
+//
+// The only way to create invalid parameters is to create a struct literal with default
+// values.
+func TestNewKeyFailsIfInvalidParams(t *testing.T) {
+	keyBytes, err := secretdata.NewBytesFromRand(32)
+	if err != nil {
+		t.Fatalf("secretdata.NewBytesFromRand(32) err = %v, want nil", err)
+	}
+	params := &aesgcm.Parameters{}
+	if _, err := aesgcm.NewKey(*keyBytes, 123, params); err == nil {
+		t.Errorf("aesgcm.NewKey(*keyBytes, 123, nil) err = nil, want error")
+	}
+}
+
 func TestOutputPrefix(t *testing.T) {
 	for _, test := range []struct {
 		name    string