Index: openmp/libomptarget/src/device.cpp
===================================================================
--- openmp/libomptarget/src/device.cpp
+++ openmp/libomptarget/src/device.cpp
@@ -229,6 +229,14 @@
       DP("Return HstPtrBegin " DPxMOD " Size=%" PRId64 " for unified shared "
          "memory\n",
          DPxPTR((uintptr_t)HstPtrBegin), Size);
+
+      if (!PM->RTLs.NoMaps)
+        // even under unified_shared_memory need to check for correctness of
+        // use of map clauses. device pointer is same as host ptr in this case
+        HostDataToTargetMap.emplace(
+            (uintptr_t)HstPtrBase, (uintptr_t)HstPtrBegin,
+            (uintptr_t)HstPtrBegin + Size, (uintptr_t)HstPtrBegin, HstPtrName);
+
       IsHostPtr = true;
       TargetPointer = HstPtrBegin;
     }
@@ -367,9 +375,6 @@
 
 int DeviceTy::deallocTgtPtr(void *HstPtrBegin, int64_t Size,
                             bool HasCloseModifier) {
-  if (PM->RTLs.RequiresFlags & OMP_REQ_UNIFIED_SHARED_MEMORY &&
-      !HasCloseModifier)
-    return OFFLOAD_SUCCESS;
   // Check if the pointer is contained in any sub-nodes.
   int rc;
   DataMapMtx.lock();
@@ -379,14 +384,17 @@
     if (HT.decRefCount() == 0) {
       DP("Deleting tgt data " DPxMOD " of size %" PRId64 "\n",
          DPxPTR(HT.TgtPtrBegin), Size);
-      deleteData((void *)HT.TgtPtrBegin);
+      if (!(PM->RTLs.RequiresFlags & OMP_REQ_UNIFIED_SHARED_MEMORY &&
+            !HasCloseModifier))
+        deleteData((void *)HT.TgtPtrBegin);
       INFO(OMP_INFOTYPE_MAPPING_CHANGED, DeviceID,
            "Removing map entry with HstPtrBegin=" DPxMOD ", TgtPtrBegin=" DPxMOD
            ", Size=%" PRId64 ", Name=%s\n",
            DPxPTR(HT.HstPtrBegin), DPxPTR(HT.TgtPtrBegin), Size,
            (HT.HstPtrName) ? getNameFromMapping(HT.HstPtrName).c_str()
                            : "unknown");
-      HostDataToTargetMap.erase(lr.Entry);
+      if (!PM->RTLs.NoMaps)
+        HostDataToTargetMap.erase(lr.Entry);
     }
     rc = OFFLOAD_SUCCESS;
   } else {
Index: openmp/libomptarget/src/rtl.h
===================================================================
--- openmp/libomptarget/src/rtl.h
+++ openmp/libomptarget/src/rtl.h
@@ -116,6 +116,8 @@
 
   int64_t RequiresFlags = OMP_REQ_UNDEFINED;
 
+  bool NoMaps;
+
   explicit RTLsTy() = default;
 
   // Register the clauses of the requires directive.
Index: openmp/libomptarget/src/rtl.cpp
===================================================================
--- openmp/libomptarget/src/rtl.cpp
+++ openmp/libomptarget/src/rtl.cpp
@@ -77,6 +77,12 @@
     return;
   }
 
+  // In UNIFIED_SHARED_MEMORY mode, users can disable
+  // map checks by setting OPENMP_DISABLE_MAPS
+  if (const char *NoMapsStr = getenv("OPENMP_DISABLE_MAPS"))
+    if (NoMapsStr)
+      NoMaps = std::stoi(NoMapsStr);
+
   DP("Loading RTLs...\n");
 
   // Attempt to open all the plugins and, if they exist, check if the interface
Index: openmp/libomptarget/test/unified_shared_memory/check_maps.c
===================================================================
--- /dev/null
+++ openmp/libomptarget/test/unified_shared_memory/check_maps.c
@@ -0,0 +1,44 @@
+// RUN: %libomptarget-compile-generic
+// RUN: %libomptarget-run-fail-generic 2>&1 \
+// RUN: | %fcheck-generic
+
+// CHECK: Libomptarget message: explicit extension not allowed: host address specified is 0x{{.*}}, but device allocation maps to host at 0x{{.*}}
+// CHECK: Libomptarget error: Call to getOrAllocTgtPtr returned null pointer (device failure or illegal mapping).
+// CHECK: Libomptarget fatal error 1: failure of target construct while offloading is mandatory
+
+// REQUIRES: unified_shared_memory
+
+#include <stdio.h>
+#include <omp.h>
+
+// ---------------------------------------------------------------------------
+// Various definitions copied from OpenMP RTL
+
+extern void __tgt_register_requires(int64_t);
+
+// End of definitions copied from OpenMP RTL.
+// ---------------------------------------------------------------------------
+
+#pragma omp requires unified_shared_memory
+
+#define N 1024
+
+int main(int argc, char *argv[]) {
+  int data[N];
+
+  // Manual registration of requires flags for Clang versions
+  // that do not support requires.
+  __tgt_register_requires(8);
+
+
+#pragma omp target enter data map(to:data[0:N/2])
+
+// extending a map under unified_shared_memory mode is prohibited
+#pragma omp target enter data map(to:data[0:N])
+
+#pragma omp target
+  {
+  }
+
+  return 0;
+}