diff --git a/src/coreclr/jit/gentree.cpp b/src/coreclr/jit/gentree.cpp
index 3af72048706405..9f7b822af7530d 100644
--- a/src/coreclr/jit/gentree.cpp
+++ b/src/coreclr/jit/gentree.cpp
@@ -9059,12 +9059,18 @@ GenTreeQmark* Compiler::gtNewQmarkNode(var_types type, GenTree* cond, GenTreeCol
 GenTreeIntCon* Compiler::gtNewIconNode(ssize_t value, var_types type)
 {
     assert(genActualType(type) == type);
+    // For TYP_INT-sized constants the value must fit in int32_t; otherwise the
+    // node is in an invalid state and downstream SetIconValue / BashToConst
+    // will assert when the constant is updated. Wider values should use
+    // gtNewLconNode (TYP_LONG) or TYP_I_IMPL on 64-bit targets.
+    assert(genTypeSize(type) > genTypeSize(TYP_INT) || FitsIn<int32_t>(value));
     return new (this, GT_CNS_INT) GenTreeIntCon(type, value);
 }
 
 GenTreeIntCon* Compiler::gtNewIconNodeWithVN(Compiler* comp, ssize_t value, var_types type)
 {
     assert(genActualType(type) == type);
+    assert(genTypeSize(type) > genTypeSize(TYP_INT) || FitsIn<int32_t>(value));
     GenTreeIntCon* cns = new (this, GT_CNS_INT) GenTreeIntCon(type, value);
     comp->fgUpdateConstTreeValueNumber(cns);
     return cns;
diff --git a/src/coreclr/jit/importercalls.cpp b/src/coreclr/jit/importercalls.cpp
index 851e08288b3d35..1a8c83a0c6905e 100644
--- a/src/coreclr/jit/importercalls.cpp
+++ b/src/coreclr/jit/importercalls.cpp
@@ -6408,7 +6408,13 @@ GenTree* Compiler::impPrimitiveNamedIntrinsic(NamedIntrinsic        intrinsic,
                 else
                 {
                     uint32_t cns1 = static_cast<uint32_t>(op1->AsIntConCommon()->IconValue());
-                    result        = gtNewIconNode(BitOperations::RotateLeft(cns1, cns2), baseType);
+                    // Sign-extend the unsigned fold result to int32_t so that downstream
+                    // SetIconValue / BashToConst calls (which assert FitsIn<int32_t> for
+                    // TYP_INT-sized constants) don't trip on the high-bit-set case
+                    // (e.g. RotateLeft(0xFFFFFFFFu, k) -> 0xFFFFFFFF zero-extended to a
+                    // positive ssize_t that doesn't fit in int32_t).
+                    result        = gtNewIconNode(
+                        static_cast<int32_t>(BitOperations::RotateLeft(cns1, cns2)), baseType);
                 }
                 break;
             }
@@ -6457,7 +6463,13 @@ GenTree* Compiler::impPrimitiveNamedIntrinsic(NamedIntrinsic        intrinsic,
                 else
                 {
                     uint32_t cns1 = static_cast<uint32_t>(op1->AsIntConCommon()->IconValue());
-                    result        = gtNewIconNode(BitOperations::RotateRight(cns1, cns2), baseType);
+                    // Sign-extend the unsigned fold result to int32_t so that downstream
+                    // SetIconValue / BashToConst calls (which assert FitsIn<int32_t> for
+                    // TYP_INT-sized constants) don't trip on the high-bit-set case
+                    // (e.g. RotateRight(0xFFFFFFFFu, k) -> 0xFFFFFFFF zero-extended to a
+                    // positive ssize_t that doesn't fit in int32_t).
+                    result        = gtNewIconNode(
+                        static_cast<int32_t>(BitOperations::RotateRight(cns1, cns2)), baseType);
                 }
                 break;
             }
diff --git a/src/tests/JIT/Regression/JitBlue/Runtime_129099/Runtime_129099.cs b/src/tests/JIT/Regression/JitBlue/Runtime_129099/Runtime_129099.cs
new file mode 100644
index 00000000000000..b05ef51e287e74
--- /dev/null
+++ b/src/tests/JIT/Regression/JitBlue/Runtime_129099/Runtime_129099.cs
@@ -0,0 +1,67 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// NI_PRIMITIVE_RotateLeft/Right's const-fold path stored the unsigned
+// fold result into a TYP_INT/TYP_UINT GenTreeIntCon via gtNewIconNode.
+// For uint operands with the high bit set (e.g. RotateRight(0xFFFFFFFFu, k))
+// the zero-extended ssize_t value (0xFFFFFFFF = 4294967295) does not fit
+// in int32_t, tripping a downstream FitsIn<int32_t> assert during
+// 'Morph - Global' when the constant was bashed/updated.
+//
+// The volatile Sink is required so the fold result is materialized as a
+// store (rather than dropped or inlined into the return path) -- that
+// store is what hits the wide-value assert.
+
+namespace Runtime_129099;
+
+using System.Numerics;
+using System.Runtime.CompilerServices;
+using Xunit;
+
+public static class Runtime_129099
+{
+    private static volatile uint SinkU32;
+    private static volatile int SinkI32;
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static uint FoldRotateRightUInt()
+    {
+        uint v = BitOperations.RotateRight(0xFFFFFFFFu, 1);
+        SinkU32 = v;
+        return v;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static uint FoldRotateLeftUInt()
+    {
+        uint v = BitOperations.RotateLeft(0xFFFFFFFFu, 1);
+        SinkU32 = v;
+        return v;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static uint FoldRotateRightHighBit()
+    {
+        uint v = BitOperations.RotateRight(0x80000000u, 3);
+        SinkU32 = v;
+        return v;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public static int FoldIntRotateRightMinusOne()
+    {
+        int v = int.RotateRight(-1, 3);
+        SinkI32 = v;
+        return v;
+    }
+
+    [Fact]
+    public static int TestEntryPoint()
+    {
+        if (FoldRotateRightUInt()      != 0xFFFFFFFFu) return 101;
+        if (FoldRotateLeftUInt()       != 0xFFFFFFFFu) return 102;
+        if (FoldRotateRightHighBit()   != 0x10000000u) return 103;
+        if (FoldIntRotateRightMinusOne() != -1)        return 104;
+        return 100;
+    }
+}
diff --git a/src/tests/JIT/Regression/Regression_ro_2.csproj b/src/tests/JIT/Regression/Regression_ro_2.csproj
index 82e13ec3df7e5c..c53c1ef89dd13b 100644
--- a/src/tests/JIT/Regression/Regression_ro_2.csproj
+++ b/src/tests/JIT/Regression/Regression_ro_2.csproj
@@ -101,6 +101,7 @@
     <Compile Include="JitBlue\Runtime_128631\Runtime_128631.cs" />
     <Compile Include="JitBlue\Runtime_128801\Runtime_128801.cs" />
     <Compile Include="JitBlue\Runtime_129076\Runtime_129076.cs" />
+    <Compile Include="JitBlue\Runtime_129099\Runtime_129099.cs" />
   </ItemGroup>
   <Import Project="$(TestSourceDir)MergedTestRunner.targets" />
 </Project>