diff --git a/truffle/docs/bytecode_dsl/UserGuide.md b/truffle/docs/bytecode_dsl/UserGuide.md
index 7815a79e64a8..d04951b4b911 100644
--- a/truffle/docs/bytecode_dsl/UserGuide.md
+++ b/truffle/docs/bytecode_dsl/UserGuide.md
@@ -303,7 +303,8 @@ These helpers often have extra indirection, so the built-in operations and acces
 
 Local reads/writes should always use these abstractions; **you should not directly read from or write to the frame**.
 
-It is undefined behaviour to load a local before a value is stored into it.
+Loading a local before a value is stored into it throws a [`FrameSlotTypeException`](https://github.com/oracle/graal/blob/master/truffle/src/com.oracle.truffle.api/src/com/oracle/truffle/api/frame/FrameSlotTypeException.java).
+You can specify a `defaultLocalValue` in [`@GenerateBytecode`](https://github.com/oracle/graal/blob/master/truffle/src/com.oracle.truffle.api.bytecode/src/com/oracle/truffle/api/bytecode/GenerateBytecode.java) to instead give uninitialized locals a default value.
 
 
 ### Scoping
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterBase.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterBase.java
index c24c672eab73..786bf283a28c 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterBase.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterBase.java
@@ -3249,6 +3249,7 @@ long continueAt(BasicInterpreterBase $root, VirtualFrame frame, VirtualFrame loc
             int op;
             long temp;
             LoopCounter loopCounter = new LoopCounter();
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -6012,7 +6013,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterUnsafe.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterUnsafe.java
index 06ca13159d38..01a63b169027 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterUnsafe.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterUnsafe.java
@@ -3249,6 +3249,7 @@ long continueAt(BasicInterpreterUnsafe $root, VirtualFrame frame, VirtualFrame l
             int op;
             long temp;
             LoopCounter loopCounter = new LoopCounter();
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -6012,7 +6013,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithBE.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithBE.java
index 47ef9179c832..10f99440410f 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithBE.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithBE.java
@@ -4959,6 +4959,7 @@ long continueAt(BasicInterpreterWithBE $root, VirtualFrame frame, VirtualFrame l
             int op;
             long temp;
             LoopCounter loopCounter = new LoopCounter();
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -10041,7 +10042,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithOptimizations.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithOptimizations.java
index ffe2418b1363..53673775c142 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithOptimizations.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithOptimizations.java
@@ -3245,6 +3245,7 @@ long continueAt(BasicInterpreterWithOptimizations $root, VirtualFrame frame, Vir
             int op;
             long temp;
             LoopCounter loopCounter = new LoopCounter();
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -6009,7 +6010,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal produces the default local value (LOCAL_DEFAULT_VALUE).
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithStoreBytecodeIndexInFrame.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithStoreBytecodeIndexInFrame.java
index 0f489a44ecbc..c27be69ba69a 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithStoreBytecodeIndexInFrame.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithStoreBytecodeIndexInFrame.java
@@ -4975,6 +4975,7 @@ long continueAt(BasicInterpreterWithStoreBytecodeIndexInFrame $root, VirtualFram
             int op;
             long temp;
             LoopCounter loopCounter = new LoopCounter();
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -8728,6 +8729,7 @@ long continueAt(BasicInterpreterWithStoreBytecodeIndexInFrame $root, VirtualFram
                 int sp = (short) (startState >>> 32);
                 int op;
                 long temp;
+                CompilerAsserts.partialEvaluationConstant(bci);
                 loop: while (true) {
                     op = BYTES.getShort(bc, bci);
                     try {
@@ -11241,7 +11243,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithUncached.java b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithUncached.java
index 6c8117a92d42..b2d60562af68 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithUncached.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.api.bytecode.test/src_gen/com/oracle/truffle/api/bytecode/test/basic_interpreter/BasicInterpreterWithUncached.java
@@ -3261,6 +3261,7 @@ long continueAt(BasicInterpreterWithUncached $root, VirtualFrame frame, VirtualF
             long temp;
             LoopCounter loopCounter = new LoopCounter();
             FRAMES.setInt(localFrame, BCI_INDEX, -1);
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -4743,6 +4744,7 @@ long continueAt(BasicInterpreterWithUncached $root, VirtualFrame frame, VirtualF
                 int sp = (short) (startState >>> 32);
                 int op;
                 long temp;
+                CompilerAsserts.partialEvaluationConstant(bci);
                 loop: while (true) {
                     op = BYTES.getShort(bc, bci);
                     try {
@@ -7033,7 +7035,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/mxbuild/jdk21/com.oracle.truffle.sl/src_gen/com/oracle/truffle/sl/bytecode/SLBytecodeRootNodeGen.java b/truffle/mxbuild/jdk21/com.oracle.truffle.sl/src_gen/com/oracle/truffle/sl/bytecode/SLBytecodeRootNodeGen.java
index 417ada8789ff..2bc9f6d3967e 100644
--- a/truffle/mxbuild/jdk21/com.oracle.truffle.sl/src_gen/com/oracle/truffle/sl/bytecode/SLBytecodeRootNodeGen.java
+++ b/truffle/mxbuild/jdk21/com.oracle.truffle.sl/src_gen/com/oracle/truffle/sl/bytecode/SLBytecodeRootNodeGen.java
@@ -4347,6 +4347,7 @@ long continueAt(SLBytecodeRootNodeGen $root, VirtualFrame frame, long startState
             long temp;
             LoopCounter loopCounter = new LoopCounter();
             FRAMES.setInt(frame, BCI_INDEX, -1);
+            CompilerAsserts.partialEvaluationConstant(bci);
             loop: while (true) {
                 op = BYTES.getShort(bc, bci);
                 try {
@@ -7617,6 +7618,7 @@ long continueAt(SLBytecodeRootNodeGen $root, VirtualFrame frame, long startState
                 int sp = (short) (startState >>> 32);
                 int op;
                 long temp;
+                CompilerAsserts.partialEvaluationConstant(bci);
                 loop: while (true) {
                     op = BYTES.getShort(bc, bci);
                     try {
@@ -9760,7 +9762,7 @@ private void validateLocalScope(BytecodeLocal local) {
          * Signature: LoadLocal() -> Object
          * <p>
          * LoadLocal reads {@code local} from the current frame.
-         * If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
+         * If a value has not been written to the local, LoadLocal throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}.
          *
          * @param local the local to load.
          */
diff --git a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
index 55d22161630e..eacc8a41a2cf 100644
--- a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
+++ b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/generator/BytecodeRootNodeElement.java
@@ -12816,6 +12816,8 @@ private List<CodeExecutableElement> createContinueAt() {
                 b.statement("FRAMES.setInt(" + localFrame() + ", " + BCI_INDEX + ", -1)");
             }
 
+            b.startStatement().startStaticCall(types.CompilerAsserts, "partialEvaluationConstant").string("bci").end().end();
+
             b.string("loop: ").startWhile().string("true").end().startBlock();
 
             // filtered instructions
diff --git a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/model/BytecodeDSLBuiltins.java b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/model/BytecodeDSLBuiltins.java
index 59769217a8a0..8b4913622f32 100644
--- a/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/model/BytecodeDSLBuiltins.java
+++ b/truffle/src/com.oracle.truffle.dsl.processor/src/com/oracle/truffle/dsl/processor/bytecode/model/BytecodeDSLBuiltins.java
@@ -244,10 +244,10 @@ Conditional implements a conditional expression (e.g., {@code condition ? thens
                         .setInstruction(m.instruction(InstructionKind.LOAD_EXCEPTION, "load.exception", m.signature(Object.class))//
                                         .addImmediate(ImmediateKind.STACK_POINTER, "exception_sp"));
         m.loadLocalOperation = m.operation(OperationKind.LOAD_LOCAL, "LoadLocal",
-                        """
+                        String.format("""
                                         LoadLocal reads {@code local} from the current frame.
-                                        If a value has not been written to the local, LoadLocal produces the default value as defined in the {@link FrameDescriptor} ({@code null} by default).
-                                        """) //
+                                        If a value has not been written to the local, LoadLocal %s.
+                                        """, loadLocalUndefinedBehaviour(m))) //
                         .setOperationBeginArguments(new OperationArgument(types.BytecodeLocal, Encoding.LOCAL, "local", "the local to load")) //
                         .setInstruction(m.instruction(InstructionKind.LOAD_LOCAL, "load.local", m.signature(Object.class)) //
                                         .addImmediate(ImmediateKind.LOCAL_OFFSET, "local_offset"));
@@ -372,6 +372,14 @@ public static void addCheckBooleanInstruction(BytecodeDSLModel m) {
         }
     }
 
+    private static String loadLocalUndefinedBehaviour(BytecodeDSLModel m) {
+        if (m.defaultLocalValue == null || m.defaultLocalValue.isEmpty()) {
+            return "throws a {@link com.oracle.truffle.api.frame.FrameSlotTypeException}";
+        } else {
+            return String.format("produces the default local value (%s)", m.defaultLocalValue);
+        }
+    }
+
     private static DynamicOperandModel child(String name) {
         return new DynamicOperandModel(List.of(name), false, false);
     }