diff --git a/CMakeLists.txt b/CMakeLists.txt
index af7b28979..d7ae17b8f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -129,14 +129,11 @@ SET_SOURCE_FILES_PROPERTIES(src/fish_version.cpp
 
 OPTION(INTERNAL_WCWIDTH "use fallback wcwidth" ON)
 IF(INTERNAL_WCWIDTH)
-    ADD_DEFINITIONS(-DHAVE_BROKEN_WCWIDTH=1)
+    add_definitions(-DHAVE_BROKEN_WCWIDTH=1)
 ELSE()
-    ADD_DEFINITIONS(-DHAVE_BROKEN_WCWIDTH=0)
+    add_definitions(-DHAVE_BROKEN_WCWIDTH=0)
 ENDIF()
 
-# Enable thread-safe errno on Solaris (#5611)
-ADD_DEFINITIONS(-D_POSIX_C_SOURCE=200809L)
-
 # Set up PCRE2
 INCLUDE(cmake/PCRE2.cmake)