diff --git a/packages/safe-ds-lang/src/language/validation/safe-ds-validator.ts b/packages/safe-ds-lang/src/language/validation/safe-ds-validator.ts
index f0deb8749..1bd88d35f 100644
--- a/packages/safe-ds-lang/src/language/validation/safe-ds-validator.ts
+++ b/packages/safe-ds-lang/src/language/validation/safe-ds-validator.ts
@@ -166,11 +166,13 @@ import {
     listMustNotContainNamedTuples,
     mapMustNotContainNamedTuples,
     namedTypeMustSetAllTypeParameters,
+    namedTypeTypeArgumentsMustMatchBounds,
     parameterDefaultValueTypeMustMatchParameterType,
     parameterMustHaveTypeHint,
     prefixOperationOperandMustHaveCorrectType,
     resultMustHaveTypeHint,
     typeCastExpressionMustHaveUnknownType,
+    typeParameterDefaultValueMustMatchUpperBound,
     yieldTypeMustMatchResultType,
 } from './types.js';
 import { statementMustDoSomething } from './other/statements/statements.js';
@@ -313,6 +315,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
             namedTypeMustSetAllTypeParameters(services),
             namedTypeTypeArgumentListShouldBeNeeded(services),
             namedTypeTypeArgumentListMustNotHavePositionalArgumentsAfterNamedArguments,
+            namedTypeTypeArgumentsMustMatchBounds(services),
         ],
         SdsParameter: [
             constantParameterMustHaveConstantDefaultValue(services),
@@ -347,6 +350,7 @@ export const registerValidationChecks = function (services: SafeDsServices) {
         SdsTemplateString: [templateStringMustHaveExpressionBetweenTwoStringParts],
         SdsTypeCast: [typeCastExpressionMustHaveUnknownType(services)],
         SdsTypeParameter: [
+            typeParameterDefaultValueMustMatchUpperBound(services),
             typeParameterMustBeUsedInCorrectPosition(services),
             typeParameterMustHaveSufficientContext,
             typeParameterMustOnlyBeVariantOnClass,
diff --git a/packages/safe-ds-lang/src/language/validation/types.ts b/packages/safe-ds-lang/src/language/validation/types.ts
index f5d751867..75ea66e0b 100644
--- a/packages/safe-ds-lang/src/language/validation/types.ts
+++ b/packages/safe-ds-lang/src/language/validation/types.ts
@@ -22,6 +22,7 @@ import {
     SdsPrefixOperation,
     SdsResult,
     SdsTypeCast,
+    SdsTypeParameter,
     SdsYield,
 } from '../generated/ast.js';
 import { getTypeArguments, getTypeParameters, TypeParameter } from '../helpers/nodeProperties.js';
@@ -251,6 +252,44 @@ export const mapMustNotContainNamedTuples = (services: SafeDsServices) => {
     };
 };
 
+export const namedTypeTypeArgumentsMustMatchBounds = (services: SafeDsServices) => {
+    const nodeMapper = services.helpers.NodeMapper;
+    const typeChecker = services.types.TypeChecker;
+    const typeComputer = services.types.TypeComputer;
+
+    return (node: SdsNamedType, accept: ValidationAcceptor): void => {
+        const type = typeComputer.computeType(node);
+        if (!(type instanceof ClassType) || isEmpty(type.substitutions)) {
+            return;
+        }
+
+        for (const typeArgument of getTypeArguments(node)) {
+            const typeParameter = nodeMapper.typeArgumentToTypeParameter(typeArgument);
+            if (!typeParameter) {
+                continue;
+            }
+
+            const typeArgumentType = type.substitutions.get(typeParameter);
+            if (!typeArgumentType) {
+                /* c8 ignore next 2 */
+                continue;
+            }
+
+            const upperBound = typeComputer
+                .computeUpperBound(typeParameter, { stopAtTypeParameterType: true })
+                .substituteTypeParameters(type.substitutions);
+
+            if (!typeChecker.isSubtypeOf(typeArgumentType, upperBound, { strictTypeParameterTypeCheck: true })) {
+                accept('error', `Expected type '${upperBound}' but got '${typeArgumentType}'.`, {
+                    node: typeArgument,
+                    property: 'value',
+                    code: CODE_TYPE_MISMATCH,
+                });
+            }
+        }
+    };
+};
+
 export const parameterDefaultValueTypeMustMatchParameterType = (services: SafeDsServices) => {
     const typeChecker = services.types.TypeChecker;
     const typeComputer = services.types.TypeComputer;
@@ -326,6 +365,28 @@ export const typeCastExpressionMustHaveUnknownType = (services: SafeDsServices)
     };
 };
 
+export const typeParameterDefaultValueMustMatchUpperBound = (services: SafeDsServices) => {
+    const typeChecker = services.types.TypeChecker;
+    const typeComputer = services.types.TypeComputer;
+
+    return (node: SdsTypeParameter, accept: ValidationAcceptor): void => {
+        if (!node.defaultValue || !node.upperBound) {
+            return;
+        }
+
+        const defaultValueType = typeComputer.computeType(node.defaultValue);
+        const upperBoundType = typeComputer.computeUpperBound(node, { stopAtTypeParameterType: true });
+
+        if (!typeChecker.isSubtypeOf(defaultValueType, upperBoundType, { strictTypeParameterTypeCheck: true })) {
+            accept('error', `Expected type '${upperBoundType}' but got '${defaultValueType}'.`, {
+                node,
+                property: 'defaultValue',
+                code: CODE_TYPE_MISMATCH,
+            });
+        }
+    };
+};
+
 export const yieldTypeMustMatchResultType = (services: SafeDsServices) => {
     const typeChecker = services.types.TypeChecker;
     const typeComputer = services.types.TypeComputer;
diff --git a/packages/safe-ds-lang/tests/resources/validation/types/checking/default values/with type parameters.sdstest b/packages/safe-ds-lang/tests/resources/validation/types/checking/default values/with type parameters.sdstest
new file mode 100644
index 000000000..5b48a14ae
--- /dev/null
+++ b/packages/safe-ds-lang/tests/resources/validation/types/checking/default values/with type parameters.sdstest	
@@ -0,0 +1,19 @@
+package tests.validation.types.checking.defaultValues
+
+class SomeClass<T1, T2 sub Number>(
+    // $TEST$ no error r"Expected type .* but got .*\."
+    p1: T1 = »true«,
+    // $TEST$ no error r"Expected type .* but got .*\."
+    p2: T1 = »1«,
+    // $TEST$ error "Expected type 'T2' but got 'literal<"">'."
+    p3: T2 = »""«,
+)
+
+fun someFunction<T1, T2 sub Number>(
+    // $TEST$ no error r"Expected type .* but got .*\."
+    p1: T1 = »true«,
+    // $TEST$ no error r"Expected type .* but got .*\."
+    p2: T1 = »1«,
+    // $TEST$ error "Expected type 'T2' but got 'literal<"">'."
+    p3: T2 = »""«,
+)
diff --git a/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for default values/main.sdstest b/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for default values/main.sdstest
new file mode 100644
index 000000000..d56a1d0d1
--- /dev/null
+++ b/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for default values/main.sdstest	
@@ -0,0 +1,57 @@
+package tests.validation.types.checking.typeParameterBoundsForDefaultValues
+
+class C1<
+    T1 sub Any,
+    // $TEST$ error "Expected type 'Number' but got 'T1'."
+    T2 sub Number = »T1«,
+    // $TEST$ error "Expected type 'Number' but got 'Any'."
+    T3 sub Number = »Any«,
+    // $TEST$ error "Expected type 'T1' but got 'Any'."
+    T4 sub T1 = »Any«,
+>
+class C2<
+    T1 sub Number,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T2 sub Number = »T1«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T3 sub Number = »Number«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T4 sub T1 = »T1«,
+>
+class C3<
+    T1 sub Int,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T2 sub Number = »T1«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T3 sub Number = »Int«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T4 sub T1 = »Nothing«,
+>
+
+@Pure fun f1<
+    T1 sub Any,
+    // $TEST$ error "Expected type 'Number' but got 'T1'."
+    T2 sub Number = »T1«,
+    // $TEST$ error "Expected type 'Number' but got 'Any'."
+    T3 sub Number = »Any«,
+    // $TEST$ error "Expected type 'T1' but got 'Any'."
+    T4 sub T1 = »Any«,
+>()
+@Pure fun f2<
+    T1 sub Number,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T2 sub Number = »T1«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T3 sub Number = »Number«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T4 sub T1 = »T1«,
+>()
+@Pure fun f3<
+    T1 sub Int,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T2 sub Number = »T1«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T3 sub Number = »Int«,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    T4 sub T1 = »Nothing«,
+>()
diff --git a/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for named types/main.sdstest b/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for named types/main.sdstest
new file mode 100644
index 000000000..d0524371e
--- /dev/null
+++ b/packages/safe-ds-lang/tests/resources/validation/types/checking/type parameter bounds for named types/main.sdstest	
@@ -0,0 +1,29 @@
+package tests.validation.types.checking.typeParameterBoundsForNamedTypes
+
+class C1<T1>
+class C2<T1 sub Number>
+class C3<T1, T2 sub T1>
+
+@Pure fun f(
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    a1: C1<»Any?«>,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    a2: C1<T1 = »Any?«>,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    a3: C1<Unknown = »Any?«>,
+
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    b1: C2<»Number«>,
+    // $TEST$ error "Expected type 'Number' but got 'String'."
+    b2: C2<»String«>,
+
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    c1: C3<»Number«, »Number«>,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    c2: C3<»Number«, »Int«>,
+    // $TEST$ no error r"Expected type '.*' but got '.*'\."
+    // $TEST$ error "Expected type 'Int' but got 'Number'."
+    c3: C3<»Int«, »Number«>,
+)