diff --git a/cmake/ConfigureChecks.cmake b/cmake/ConfigureChecks.cmake
index 4313582dc..22b0066a0 100644
--- a/cmake/ConfigureChecks.cmake
+++ b/cmake/ConfigureChecks.cmake
@@ -19,11 +19,6 @@ if (CMAKE_HOST_SYSTEM_VERSION MATCHES ".*-Microsoft")
   SET(WSL 1)
 endif()
 
-# Detect Cygwin.
-if (CMAKE_SYSTEM_NAME MATCHES "CYGWIN_NT.*")
-  SET(CYGWIN 1)
-endif()
-
 # Set up the config.h file.
 SET(PACKAGE_NAME "fish")
 SET(PACKAGE_TARNAME "fish")
diff --git a/config_cmake.h.in b/config_cmake.h.in
index 2c6fde27d..8071546fd 100644
--- a/config_cmake.h.in
+++ b/config_cmake.h.in
@@ -4,9 +4,6 @@
 /* Define to 1 if compiled on WSL */
 #cmakedefine WSL 1
 
-/* Define to 1 if complied under Cygwin */
-#cmakedefine CYGWIN 1
-
 /* Define to 1 if you have the `clock_gettime' function. */
 #cmakedefine HAVE_CLOCK_GETTIME 1
 
diff --git a/src/common.h b/src/common.h
index d0436ff59..f0a4be570 100644
--- a/src/common.h
+++ b/src/common.h
@@ -978,7 +978,7 @@ constexpr bool is_windows_subsystem_for_linux() {
 
 /// Detect if we are running under Cygwin or Cgywin64
 constexpr bool is_cygwin() {
-#ifdef CYGWIN
+#ifdef __CYGWIN__
     return true;
 #else
     return false;