diff --git a/openmp/runtime/src/kmp.h b/openmp/runtime/src/kmp.h
--- a/openmp/runtime/src/kmp.h
+++ b/openmp/runtime/src/kmp.h
@@ -4072,6 +4072,18 @@
 #define KMP_GTID_TO_SHADOW_GTID(gtid)                                          \
   ((gtid) % (__kmp_hidden_helper_threads_num - 1) + 2)
 
+// Return the adjusted gtid value by subtracting from gtid the number
+// of hidden helper threads. This adjusted value is the gtid the thread would
+// have received if there were no hidden helper threads.
+static inline int __kmp_adjust_gtid_for_hidden_helpers(int gtid) {
+  int adjusted_gtid = gtid;
+  if (__kmp_enable_hidden_helper && __kmp_hidden_helper_threads_num > 0 &&
+      gtid > 0 && adjusted_gtid - __kmp_hidden_helper_threads_num >= 0) {
+    adjusted_gtid -= __kmp_hidden_helper_threads_num;
+  }
+  return adjusted_gtid;
+}
+
 // Support for error directive
 typedef enum kmp_severity_t {
   severity_warning = 1,
diff --git a/openmp/runtime/src/kmp_affinity.cpp b/openmp/runtime/src/kmp_affinity.cpp
--- a/openmp/runtime/src/kmp_affinity.cpp
+++ b/openmp/runtime/src/kmp_affinity.cpp
@@ -3950,8 +3950,9 @@
       i = 0;
       mask = __kmp_affin_fullMask;
     } else {
+      int mask_idx = __kmp_adjust_gtid_for_hidden_helpers(gtid);
       KMP_DEBUG_ASSERT(__kmp_affinity_num_masks > 0);
-      i = (gtid + __kmp_affinity_offset) % __kmp_affinity_num_masks;
+      i = (mask_idx + __kmp_affinity_offset) % __kmp_affinity_num_masks;
       mask = KMP_CPU_INDEX(__kmp_affinity_masks, i);
     }
   } else {
@@ -3967,9 +3968,10 @@
       mask = __kmp_affin_fullMask;
     } else {
       // int i = some hash function or just a counter that doesn't
-      // always start at 0.  Use gtid for now.
+      // always start at 0.  Use adjusted gtid for now.
+      int mask_idx = __kmp_adjust_gtid_for_hidden_helpers(gtid);
       KMP_DEBUG_ASSERT(__kmp_affinity_num_masks > 0);
-      i = (gtid + __kmp_affinity_offset) % __kmp_affinity_num_masks;
+      i = (mask_idx + __kmp_affinity_offset) % __kmp_affinity_num_masks;
       mask = KMP_CPU_INDEX(__kmp_affinity_masks, i);
     }
   }