diff --git a/reactos/lib/rtl/bitmap.c b/reactos/lib/rtl/bitmap.c
index c7aa880bc1e..ddb6b156042 100644
--- a/reactos/lib/rtl/bitmap.c
+++ b/reactos/lib/rtl/bitmap.c
@@ -362,8 +362,11 @@ RtlClearBits(
 
     /* Clear what's left */
     NumberToClear &= (_BITCOUNT - 1);
-    Mask = MAXINDEX << NumberToClear;
-    *Buffer &= Mask;
+    if (NumberToClear)
+    {
+        Mask = MAXINDEX << NumberToClear;
+        *Buffer &= Mask;
+    }
 }
 
 VOID
@@ -419,8 +422,11 @@ RtlSetBits(
 
     /* Set what's left */
     NumberToSet &= (_BITCOUNT - 1);
-    Mask = MAXINDEX << NumberToSet;
-    *Buffer |= ~Mask;
+    if (NumberToSet)
+    {
+        Mask = MAXINDEX << NumberToSet;
+        *Buffer |= ~Mask;
+    }
 }
 
 BOOLEAN
diff --git a/rostests/apitests/ntdll/RtlBitmap.c b/rostests/apitests/ntdll/RtlBitmap.c
index 70e0b7afb5c..99ff3a9806a 100644
--- a/rostests/apitests/ntdll/RtlBitmap.c
+++ b/rostests/apitests/ntdll/RtlBitmap.c
@@ -200,6 +200,11 @@ Test_RtlClearBits(void)
     ok_hex(Buffer[0], 0x00001fff);
     ok_hex(Buffer[1], 0xfffffff8);
 
+    memset(Buffer, 0xff, BufferSize);
+    RtlClearBits(&BitMapHeader, 63, 1);
+    ok_hex(Buffer[0], 0xffffffff);
+    ok_hex(Buffer[1], 0x7fffffff);
+
     memset(Buffer, 0xcc, BufferSize);
     RtlClearBits(&BitMapHeader, 3, 6);
     RtlClearBits(&BitMapHeader, 11, 5);
@@ -245,6 +250,11 @@ Test_RtlSetBits(void)
     ok_hex(Buffer[0], 0xffffe000);
     ok_hex(Buffer[1], 0x00000007);
 
+    memset(Buffer, 0x00, BufferSize);
+    RtlSetBits(&BitMapHeader, 63, 1);
+    ok_hex(Buffer[0], 0x00000000);
+    ok_hex(Buffer[1], 0x80000000);
+
     memset(Buffer, 0xcc, BufferSize);
     RtlSetBits(&BitMapHeader, 3, 6);
     RtlSetBits(&BitMapHeader, 11, 5);