diff --git a/include/result/result_os.hpp b/include/result/result_os.hpp
index 35d1f378f..92025366d 100644
--- a/include/result/result_os.hpp
+++ b/include/result/result_os.hpp
@@ -5,10 +5,11 @@ DEFINE_HORIZON_RESULT_MODULE(Result::OS, OS);
 
 namespace Result::OS {
 	DEFINE_HORIZON_RESULT(PortNameTooLong, 30, InvalidArgument, Usage);
-	DEFINE_HORIZON_RESULT(InvalidHandle, 1015, WrongArgument, Permanent);
 	DEFINE_HORIZON_RESULT(InvalidCombination, 1006, InvalidArgument, Usage);
 	DEFINE_HORIZON_RESULT(MisalignedAddress, 1009, InvalidArgument, Usage);
 	DEFINE_HORIZON_RESULT(MisalignedSize, 1010, InvalidArgument, Usage);
+	DEFINE_HORIZON_RESULT(NotImplemented, 1012, InvalidArgument, Usage);
+	DEFINE_HORIZON_RESULT(InvalidHandle, 1015, WrongArgument, Permanent);
 	DEFINE_HORIZON_RESULT(OutOfRange, 1021, InvalidArgument, Usage);
 	DEFINE_HORIZON_RESULT(Timeout, 1022, StatusChanged, Info);
 };  // namespace Result::OS
diff --git a/src/core/services/apt.cpp b/src/core/services/apt.cpp
index 9d02bf94d..830b83777 100644
--- a/src/core/services/apt.cpp
+++ b/src/core/services/apt.cpp
@@ -34,8 +34,8 @@ namespace APTCommands {
 }
 
 void APTService::reset() {
-	// Set the default CPU time limit to 30%. Seems safe, as this is what Metroid 2 uses by default
-	cpuTimeLimit = 30;
+	// Set the default CPU time limit to 0%. Appears to be the default value on hardware
+	cpuTimeLimit = 0;
 
 	// Reset the handles for the various service objects
 	lockHandle = std::nullopt;
@@ -311,15 +311,16 @@ void APTService::setApplicationCpuTimeLimit(u32 messagePointer) {
 	u32 percentage = mem.read32(messagePointer + 8); // CPU time percentage between 5% and 89%
 	log("APT::SetApplicationCpuTimeLimit (percentage = %d%%)\n", percentage);
 
+	mem.write32(messagePointer, IPC::responseHeader(0x4F, 1, 0));
+
+	// If called with invalid parameters, the current time limit is left unchanged, and OS::NotImplemented is returned
 	if (percentage < 5 || percentage > 89 || fixed != 1) {
 		Helpers::warn("Invalid parameter passed to APT::SetApplicationCpuTimeLimit: (percentage, fixed) = (%d, %d)\n", percentage, fixed);
-		// TODO: Does the clamp operation happen? Verify with getApplicationCpuTimeLimit on hardware
-		percentage = std::clamp<u32>(percentage, 5, 89);
+		mem.write32(messagePointer + 4, Result::OS::NotImplemented);
+	} else {
+		mem.write32(messagePointer + 4, Result::Success);
+		cpuTimeLimit = percentage;
 	}
-
-	mem.write32(messagePointer, IPC::responseHeader(0x4F, 1, 0));
-	mem.write32(messagePointer + 4, Result::Success);
-	cpuTimeLimit = percentage;
 }
 
 void APTService::getApplicationCpuTimeLimit(u32 messagePointer) {
diff --git a/tests/AppCpuTimeLimit/Makefile b/tests/AppCpuTimeLimit/Makefile
new file mode 100644
index 000000000..9fc3a849e
--- /dev/null
+++ b/tests/AppCpuTimeLimit/Makefile
@@ -0,0 +1,258 @@
+#---------------------------------------------------------------------------------
+.SUFFIXES:
+#---------------------------------------------------------------------------------
+
+ifeq ($(strip $(DEVKITARM)),)
+$(error "Please set DEVKITARM in your environment. export DEVKITARM=<path to>devkitARM")
+endif
+
+TOPDIR ?= $(CURDIR)
+include $(DEVKITARM)/3ds_rules
+
+#---------------------------------------------------------------------------------
+# TARGET is the name of the output
+# BUILD is the directory where object files & intermediate files will be placed
+# SOURCES is a list of directories containing source code
+# DATA is a list of directories containing data files
+# INCLUDES is a list of directories containing header files
+# GRAPHICS is a list of directories containing graphics files
+# GFXBUILD is the directory where converted graphics files will be placed
+#   If set to $(BUILD), it will statically link in the converted
+#   files as if they were data files.
+#
+# NO_SMDH: if set to anything, no SMDH file is generated.
+# ROMFS is the directory which contains the RomFS, relative to the Makefile (Optional)
+# APP_TITLE is the name of the app stored in the SMDH file (Optional)
+# APP_DESCRIPTION is the description of the app stored in the SMDH file (Optional)
+# APP_AUTHOR is the author of the app stored in the SMDH file (Optional)
+# ICON is the filename of the icon (.png), relative to the project folder.
+#   If not set, it attempts to use one of the following (in this order):
+#     - <Project name>.png
+#     - icon.png
+#     - <libctru folder>/default_icon.png
+#---------------------------------------------------------------------------------
+TARGET		:=	AppCpuTimeLimit
+BUILD		:=	build
+SOURCES		:=	source
+DATA		:=	data
+INCLUDES	:=	include
+GRAPHICS	:=	gfx
+GFXBUILD	:=	$(BUILD)
+#ROMFS		:=	romfs
+#GFXBUILD	:=	$(ROMFS)/gfx
+APP_TITLE   := AppCpuTimeLimit
+APP_DESCRIPTION := Tests Set/GetAppCpuTimeLimit
+APP_AUTHOR  := noumidev
+
+#---------------------------------------------------------------------------------
+# options for code generation
+#---------------------------------------------------------------------------------
+ARCH	:=	-march=armv6k -mtune=mpcore -mfloat-abi=hard -mtp=soft
+
+CFLAGS	:=	-g -Wall -O2 -mword-relocations \
+			-ffunction-sections \
+			$(ARCH)
+
+CFLAGS	+=	$(INCLUDE) -D__3DS__
+
+CXXFLAGS	:= $(CFLAGS) -fno-rtti -fno-exceptions -std=gnu++11
+
+ASFLAGS	:=	-g $(ARCH)
+LDFLAGS	=	-specs=3dsx.specs -g $(ARCH) -Wl,-Map,$(notdir $*.map)
+
+LIBS	:= -lctru -lm
+
+#---------------------------------------------------------------------------------
+# list of directories containing libraries, this must be the top level containing
+# include and lib
+#---------------------------------------------------------------------------------
+LIBDIRS	:= $(CTRULIB)
+
+
+#---------------------------------------------------------------------------------
+# no real need to edit anything past this point unless you need to add additional
+# rules for different file extensions
+#---------------------------------------------------------------------------------
+ifneq ($(BUILD),$(notdir $(CURDIR)))
+#---------------------------------------------------------------------------------
+
+export OUTPUT	:=	$(CURDIR)/$(TARGET)
+export TOPDIR	:=	$(CURDIR)
+
+export VPATH	:=	$(foreach dir,$(SOURCES),$(CURDIR)/$(dir)) \
+			$(foreach dir,$(GRAPHICS),$(CURDIR)/$(dir)) \
+			$(foreach dir,$(DATA),$(CURDIR)/$(dir))
+
+export DEPSDIR	:=	$(CURDIR)/$(BUILD)
+
+CFILES		:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.c)))
+CPPFILES	:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.cpp)))
+SFILES		:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.s)))
+PICAFILES	:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.v.pica)))
+SHLISTFILES	:=	$(foreach dir,$(SOURCES),$(notdir $(wildcard $(dir)/*.shlist)))
+GFXFILES	:=	$(foreach dir,$(GRAPHICS),$(notdir $(wildcard $(dir)/*.t3s)))
+BINFILES	:=	$(foreach dir,$(DATA),$(notdir $(wildcard $(dir)/*.*)))
+
+#---------------------------------------------------------------------------------
+# use CXX for linking C++ projects, CC for standard C
+#---------------------------------------------------------------------------------
+ifeq ($(strip $(CPPFILES)),)
+#---------------------------------------------------------------------------------
+	export LD	:=	$(CC)
+#---------------------------------------------------------------------------------
+else
+#---------------------------------------------------------------------------------
+	export LD	:=	$(CXX)
+#---------------------------------------------------------------------------------
+endif
+#---------------------------------------------------------------------------------
+
+#---------------------------------------------------------------------------------
+ifeq ($(GFXBUILD),$(BUILD))
+#---------------------------------------------------------------------------------
+export T3XFILES :=  $(GFXFILES:.t3s=.t3x)
+#---------------------------------------------------------------------------------
+else
+#---------------------------------------------------------------------------------
+export ROMFS_T3XFILES	:=	$(patsubst %.t3s, $(GFXBUILD)/%.t3x, $(GFXFILES))
+export T3XHFILES		:=	$(patsubst %.t3s, $(BUILD)/%.h, $(GFXFILES))
+#---------------------------------------------------------------------------------
+endif
+#---------------------------------------------------------------------------------
+
+export OFILES_SOURCES 	:=	$(CPPFILES:.cpp=.o) $(CFILES:.c=.o) $(SFILES:.s=.o)
+
+export OFILES_BIN	:=	$(addsuffix .o,$(BINFILES)) \
+			$(PICAFILES:.v.pica=.shbin.o) $(SHLISTFILES:.shlist=.shbin.o) \
+			$(addsuffix .o,$(T3XFILES))
+
+export OFILES := $(OFILES_BIN) $(OFILES_SOURCES)
+
+export HFILES	:=	$(PICAFILES:.v.pica=_shbin.h) $(SHLISTFILES:.shlist=_shbin.h) \
+			$(addsuffix .h,$(subst .,_,$(BINFILES))) \
+			$(GFXFILES:.t3s=.h)
+
+export INCLUDE	:=	$(foreach dir,$(INCLUDES),-I$(CURDIR)/$(dir)) \
+			$(foreach dir,$(LIBDIRS),-I$(dir)/include) \
+			-I$(CURDIR)/$(BUILD)
+
+export LIBPATHS	:=	$(foreach dir,$(LIBDIRS),-L$(dir)/lib)
+
+export _3DSXDEPS	:=	$(if $(NO_SMDH),,$(OUTPUT).smdh)
+
+ifeq ($(strip $(ICON)),)
+	icons := $(wildcard *.png)
+	ifneq (,$(findstring $(TARGET).png,$(icons)))
+		export APP_ICON := $(TOPDIR)/$(TARGET).png
+	else
+		ifneq (,$(findstring icon.png,$(icons)))
+			export APP_ICON := $(TOPDIR)/icon.png
+		endif
+	endif
+else
+	export APP_ICON := $(TOPDIR)/$(ICON)
+endif
+
+ifeq ($(strip $(NO_SMDH)),)
+	export _3DSXFLAGS += --smdh=$(CURDIR)/$(TARGET).smdh
+endif
+
+ifneq ($(ROMFS),)
+	export _3DSXFLAGS += --romfs=$(CURDIR)/$(ROMFS)
+endif
+
+.PHONY: all clean
+
+#---------------------------------------------------------------------------------
+all: $(BUILD) $(GFXBUILD) $(DEPSDIR) $(ROMFS_T3XFILES) $(T3XHFILES)
+	@$(MAKE) --no-print-directory -C $(BUILD) -f $(CURDIR)/Makefile
+
+$(BUILD):
+	@mkdir -p $@
+
+ifneq ($(GFXBUILD),$(BUILD))
+$(GFXBUILD):
+	@mkdir -p $@
+endif
+
+ifneq ($(DEPSDIR),$(BUILD))
+$(DEPSDIR):
+	@mkdir -p $@
+endif
+
+#---------------------------------------------------------------------------------
+clean:
+	@echo clean ...
+	@rm -fr $(BUILD) $(TARGET).3dsx $(OUTPUT).smdh $(TARGET).elf $(GFXBUILD)
+
+#---------------------------------------------------------------------------------
+$(GFXBUILD)/%.t3x	$(BUILD)/%.h	:	%.t3s
+#---------------------------------------------------------------------------------
+	@echo $(notdir $<)
+	@tex3ds -i $< -H $(BUILD)/$*.h -d $(DEPSDIR)/$*.d -o $(GFXBUILD)/$*.t3x
+
+#---------------------------------------------------------------------------------
+else
+
+#---------------------------------------------------------------------------------
+# main targets
+#---------------------------------------------------------------------------------
+$(OUTPUT).3dsx	:	$(OUTPUT).elf $(_3DSXDEPS)
+
+$(OFILES_SOURCES) : $(HFILES)
+
+$(OUTPUT).elf	:	$(OFILES)
+
+#---------------------------------------------------------------------------------
+# you need a rule like this for each extension you use as binary data
+#---------------------------------------------------------------------------------
+%.bin.o	%_bin.h :	%.bin
+#---------------------------------------------------------------------------------
+	@echo $(notdir $<)
+	@$(bin2o)
+
+#---------------------------------------------------------------------------------
+.PRECIOUS	:	%.t3x
+#---------------------------------------------------------------------------------
+%.t3x.o	%_t3x.h :	%.t3x
+#---------------------------------------------------------------------------------
+	@echo $(notdir $<)
+	@$(bin2o)
+
+#---------------------------------------------------------------------------------
+# rules for assembling GPU shaders
+#---------------------------------------------------------------------------------
+define shader-as
+	$(eval CURBIN := $*.shbin)
+	$(eval DEPSFILE := $(DEPSDIR)/$*.shbin.d)
+	echo "$(CURBIN).o: $< $1" > $(DEPSFILE)
+	echo "extern const u8" `(echo $(CURBIN) | sed -e 's/^\([0-9]\)/_\1/' | tr . _)`"_end[];" > `(echo $(CURBIN) | tr . _)`.h
+	echo "extern const u8" `(echo $(CURBIN) | sed -e 's/^\([0-9]\)/_\1/' | tr . _)`"[];" >> `(echo $(CURBIN) | tr . _)`.h
+	echo "extern const u32" `(echo $(CURBIN) | sed -e 's/^\([0-9]\)/_\1/' | tr . _)`_size";" >> `(echo $(CURBIN) | tr . _)`.h
+	picasso -o $(CURBIN) $1
+	bin2s $(CURBIN) | $(AS) -o $*.shbin.o
+endef
+
+%.shbin.o %_shbin.h : %.v.pica %.g.pica
+	@echo $(notdir $^)
+	@$(call shader-as,$^)
+
+%.shbin.o %_shbin.h : %.v.pica
+	@echo $(notdir $<)
+	@$(call shader-as,$<)
+
+%.shbin.o %_shbin.h : %.shlist
+	@echo $(notdir $<)
+	@$(call shader-as,$(foreach file,$(shell cat $<),$(dir $<)$(file)))
+
+#---------------------------------------------------------------------------------
+%.t3x	%.h	:	%.t3s
+#---------------------------------------------------------------------------------
+	@echo $(notdir $<)
+	@tex3ds -i $< -H $*.h -d $*.d -o $*.t3x
+
+-include $(DEPSDIR)/*.d
+
+#---------------------------------------------------------------------------------------
+endif
+#---------------------------------------------------------------------------------------
diff --git a/tests/AppCpuTimeLimit/o3ds.png b/tests/AppCpuTimeLimit/o3ds.png
new file mode 100644
index 000000000..b3da7ce7b
Binary files /dev/null and b/tests/AppCpuTimeLimit/o3ds.png differ
diff --git a/tests/AppCpuTimeLimit/source/main.c b/tests/AppCpuTimeLimit/source/main.c
new file mode 100644
index 000000000..e61dc498f
--- /dev/null
+++ b/tests/AppCpuTimeLimit/source/main.c
@@ -0,0 +1,55 @@
+#include <3ds.h>
+
+#include <stdio.h>
+
+int main(int argc, char **argv) {
+    gfxInitDefault();
+
+    consoleInit(GFX_TOP, NULL);
+
+    printf("--- APT::SetAppCpuTimeLimit ---\n\n");
+
+    // Get initial percentage
+    u32 percentage;
+    APT_GetAppCpuTimeLimit(&percentage);
+
+    printf("Initial percentage: %lu\n\n", percentage);
+
+    // Try all percentages from 0-100%, print failed calls
+    for (int i = 0; i <= 100; i++) {
+        const Result res = APT_SetAppCpuTimeLimit(i);
+
+        if (R_FAILED(res)) {
+            APT_GetAppCpuTimeLimit(&percentage);
+
+            printf("[%d:%lu:%lX]\n", i, percentage, res);
+        }
+    }
+
+    // Send command with invalid fixed value
+    u32 aptcmdbuf[16];
+    aptcmdbuf[0] = 0x004F0080;
+    aptcmdbuf[1] = 0;
+    aptcmdbuf[2] = 20;
+
+    aptSendCommand(aptcmdbuf);
+
+    printf("\nWith fixed = 0: [%08lX:%08lX]\n", aptcmdbuf[0], aptcmdbuf[1]);
+
+    while (aptMainLoop()) {
+        hidScanInput();
+
+        if ((hidKeysDown() & KEY_START) != 0) {
+            break;
+        }
+
+        gfxFlushBuffers();
+        gfxSwapBuffers();
+
+        gspWaitForVBlank();
+    }
+
+    gfxExit();
+
+    return 0;
+}