diff --git a/.gitlab/ci/env_windows_pellesc13.01.ps1 b/.gitlab/ci/env_windows_pellesc13.01.ps1
index 4a8b1cad43..84a38ac83d 100644
--- a/.gitlab/ci/env_windows_pellesc13.01.ps1
+++ b/.gitlab/ci/env_windows_pellesc13.01.ps1
@@ -1,6 +1,2 @@
 . .gitlab/ci/ninja-env.ps1
 . .gitlab/ci/pellesc-env.ps1
-
-# FIXME(#21536): Avoid requiring the end user to enable
-# Pelles C's Microsoft extensions to use Windows APIs.
-$env:CFLAGS = "-Ze"
diff --git a/Modules/Platform/Windows-PellesC-ASM_POASM.cmake b/Modules/Platform/Windows-PellesC-ASM_POASM.cmake
index 2cafaef3bd..2bff21f2b7 100644
--- a/Modules/Platform/Windows-PellesC-ASM_POASM.cmake
+++ b/Modules/Platform/Windows-PellesC-ASM_POASM.cmake
@@ -6,3 +6,8 @@ __windows_compiler_pellesc(ASM_POASM)
 
 set(CMAKE_ASM_POASM_COMPILE_OBJECT
   "<CMAKE_ASM_POASM_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -Fo<OBJECT> <SOURCE>")
+
+string(APPEND CMAKE_ASM_POASM_FLAGS_DEBUG_INIT " -Zi")
+string(APPEND CMAKE_ASM_POASM_FLAGS_RELEASE_INIT "")
+string(APPEND CMAKE_ASM_POASM_FLAGS_RELWITHDEBINFO_INIT " -Zi")
+string(APPEND CMAKE_ASM_POASM_FLAGS_MINSIZEREL_INIT "")
diff --git a/Modules/Platform/Windows-PellesC-C.cmake b/Modules/Platform/Windows-PellesC-C.cmake
index 64fd5f6ecd..f5a3dad38c 100644
--- a/Modules/Platform/Windows-PellesC-C.cmake
+++ b/Modules/Platform/Windows-PellesC-C.cmake
@@ -6,3 +6,12 @@ __windows_compiler_pellesc(C)
 
 set(CMAKE_C_COMPILE_OBJECT
   "<CMAKE_C_COMPILER> <DEFINES> <INCLUDES> <FLAGS> -Fo<OBJECT> -c <SOURCE>")
+
+# Enable Pelles C's Microsoft extensions to use Windows APIs.
+# The flag also disables standard definitions, so add them.
+string(APPEND CMAKE_C_FLAGS_INIT " -Ze -D__STDC__=1 -D__STDC_VERSION__=__POCC_STDC_VERSION__")
+
+string(APPEND CMAKE_C_FLAGS_DEBUG_INIT " -Zi -Ob0")
+string(APPEND CMAKE_C_FLAGS_RELEASE_INIT " -Ot -Ob2 -DNDEBUG=1")
+string(APPEND CMAKE_C_FLAGS_RELWITHDEBINFO_INIT " -Zi -Ot -Ob1 -DNDEBUG=1")
+string(APPEND CMAKE_C_FLAGS_MINSIZEREL_INIT " -Os -Ob1 -DNDEBUG=1")
diff --git a/Modules/Platform/Windows-PellesC.cmake b/Modules/Platform/Windows-PellesC.cmake
index eb165766ac..d29cc4a4d9 100644
--- a/Modules/Platform/Windows-PellesC.cmake
+++ b/Modules/Platform/Windows-PellesC.cmake
@@ -6,6 +6,8 @@ set(CMAKE_LIBRARY_PATH_FLAG "-libpath:")
 set(CMAKE_LINK_DEF_FILE_FLAG "-def:")
 set(CMAKE_LINK_LIBRARY_FLAG "")
 
+set(CMAKE_BUILD_TYPE_INIT Debug)
+
 macro(__windows_compiler_pellesc lang)
   set(CMAKE_${lang}_CREATE_STATIC_LIBRARY "<CMAKE_AR> <LINK_FLAGS> -out:<TARGET> <OBJECTS>")
 
@@ -27,3 +29,8 @@ macro(__windows_compiler_pellesc lang)
   endif()
   enable_language(RC)
 endmacro()
+
+foreach (t IN ITEMS EXE SHARED MODULE)
+  string(APPEND CMAKE_${t}_LINKER_FLAGS_DEBUG_INIT " -debug -debugtype:both -dbg")
+  string(APPEND CMAKE_${t}_LINKER_FLAGS_RELWITHDEBINFO_INIT " -debug -debugtype:both -dbg")
+endforeach ()