diff --git a/tools/binpac/src/CMakeLists.txt b/tools/binpac/src/CMakeLists.txt
index 74920f3ea8..24529cce6e 100644
--- a/tools/binpac/src/CMakeLists.txt
+++ b/tools/binpac/src/CMakeLists.txt
@@ -106,6 +106,11 @@ set(binpac_SRCS
 add_executable(binpac ${binpac_SRCS})
 
 if ( MSVC )
+    # If building separately from zeek, we need to add the libunistd subdirectory so
+    # that linking doesn't fail.
+    if ("${CMAKE_PROJECT_NAME}" STREQUAL "BinPAC")
+        add_subdirectory(auxil/libunistd EXCLUDE_FROM_ALL)
+    endif()
     target_link_libraries(binpac PRIVATE libunistd)
 endif()