diff --git a/lib/posix/posix.nim b/lib/posix/posix.nim
index a5ee05abbd..e1bcd9dfcb 100644
--- a/lib/posix/posix.nim
+++ b/lib/posix/posix.nim
@@ -1579,6 +1579,16 @@ var
   MSG_OOB* {.importc, header: "<sys/socket.h>".}: cint
     ## Out-of-band data.
 
+
+when defined(linux):
+  var
+    MAP_POPULATE* {.importc, header: "<sys/mman.h>".}: cint
+      ## Populate (prefault) page tables for a mapping.
+else:
+  var
+    MAP_POPULATE*: cint = 0
+
+
 when defined(macosx):
   var
     MSG_HAVEMORE* {.importc, header: "<sys/socket.h>".}: cint
diff --git a/lib/pure/memfiles.nim b/lib/pure/memfiles.nim
index 31fefc6c82..ffeb0beffe 100644
--- a/lib/pure/memfiles.nim
+++ b/lib/pure/memfiles.nim
@@ -54,7 +54,7 @@ proc mapMem*(m: var TMemFile, mode: TFileMode = fmRead,
       nil,
       mappedSize,
       if readonly: PROT_READ else: PROT_READ or PROT_WRITE,
-      if readonly: MAP_PRIVATE else: MAP_SHARED,
+      if readonly: (MAP_PRIVATE or MAP_POPULATE) else: (MAP_SHARED or MAP_POPULATE),
       m.handle, offset)
     if result == cast[pointer](MAP_FAILED):
       osError(osLastError())
@@ -207,7 +207,7 @@ proc open*(filename: string, mode: TFileMode = fmRead,
       nil,
       result.size,
       if readonly: PROT_READ else: PROT_READ or PROT_WRITE,
-      if readonly: MAP_PRIVATE else: MAP_SHARED,
+      if readonly: (MAP_PRIVATE or MAP_POPULATE) else: (MAP_SHARED or MAP_POPULATE),
       result.handle,
       offset)