diff --git a/src/system/kernel/lib/Jamfile b/src/system/kernel/lib/Jamfile
index 3591b3afa9..0d5f7ffcd6 100644
--- a/src/system/kernel/lib/Jamfile
+++ b/src/system/kernel/lib/Jamfile
@@ -47,6 +47,14 @@ SEARCH_SOURCE += [ FDirName $(posixSources) time ] ;
 SEARCH_SOURCE += [ FDirName $(posixSources) unistd ] ;
 SEARCH_SOURCE += [ FDirName $(gnuSources) ] ;
 
+local muslSources =
+	ffs.c
+	;
+
+SourceHdrs $(muslSources) :
+	[ FDirName $(posixSources) musl internal ]
+	[ FDirName $(posixSources) musl arch $(TARGET_KERNEL_ARCH_DIR) ] ;
+
 KernelMergeObject kernel_lib_posix.o :
 	# main
 	kernel_errno.cpp
@@ -99,7 +107,6 @@ KernelMergeObject kernel_lib_posix.o :
 	usergroup.cpp
 	write.c
 	# string
-	ffs.cpp
 	memchr.c
 	memcmp.c
 	memmem.c
@@ -129,9 +136,12 @@ KernelMergeObject kernel_lib_posix.o :
 	strupr.c
 	stpcpy.c
 
+	$(muslSources)
 	: $(TARGET_KERNEL_PIC_CCFLAGS)
 ;
 
+SEARCH on [ FGristFiles $(muslSources) ] += [ FDirName $(posixSources) musl misc ] ;
+
 # misc
 
 SEARCH_SOURCE = [ FDirName $(HAIKU_TOP) src kits support ] ;
diff --git a/src/system/libroot/posix/musl/misc/Jamfile b/src/system/libroot/posix/musl/misc/Jamfile
index 4a4d7fb998..afa139f6c3 100644
--- a/src/system/libroot/posix/musl/misc/Jamfile
+++ b/src/system/libroot/posix/musl/misc/Jamfile
@@ -2,7 +2,7 @@ SubDir HAIKU_TOP src system libroot posix musl misc ;
 
 SubDirSysHdrs [ FDirName $(SUBDIR) .. include ] ;
 UseHeaders [ FDirName $(SUBDIR) .. internal ] ;
-UseHeaders [ FDirName $(SUBDIR) .. arch $(TARGET_KERNEL_ARCH_DIR) ] ;
+UseHeaders [ FDirName $(SUBDIR) .. arch $(TARGET_ARCH) ] ;
 
 local architectureObject ;
 for architectureObject in [ MultiArchSubDirSetup ] {
diff --git a/src/system/libroot/posix/musl/misc/ffs.c b/src/system/libroot/posix/musl/misc/ffs.c
index 240b3a101d..a202a48ac6 100644
--- a/src/system/libroot/posix/musl/misc/ffs.c
+++ b/src/system/libroot/posix/musl/misc/ffs.c
@@ -1,5 +1,6 @@
 #include "atomic.h"
 
+int ffs(int i);
 int ffs(int i)
 {
 	return i ? a_ctz_l(i)+1 : 0;