diff --git a/src/cmd/cov/Makefile b/src/cmd/cov/Makefile
index 4e02547dca..9c0d8abaa0 100644
--- a/src/cmd/cov/Makefile
+++ b/src/cmd/cov/Makefile
@@ -22,7 +22,7 @@ $(TARG): $(OFILES)
 clean:
 	rm -f $(OFILES) $(TARG)
 
-install: install-$(GOOS)
+install: install-$(shell uname | tr A-Z a-z)
 install-linux: install-default
 
 # on Darwin, have to install and setgid; see $GOROOT/src/sudo.bash
diff --git a/src/cmd/prof/Makefile b/src/cmd/prof/Makefile
index 193f5896cd..daab2df1bf 100644
--- a/src/cmd/prof/Makefile
+++ b/src/cmd/prof/Makefile
@@ -22,7 +22,7 @@ $(TARG): $(OFILES)
 clean:
 	rm -f $(OFILES) $(TARG)
 
-install: install-$(GOOS)
+install: install-$(shell uname | tr A-Z a-z)
 install-linux: install-default
 
 # on Darwin, have to install and setgid; see $GOROOT/src/sudo.bash
diff --git a/src/libmach/Makefile b/src/libmach/Makefile
index 4a5e3405fc..b0031486ab 100644
--- a/src/libmach/Makefile
+++ b/src/libmach/Makefile
@@ -45,7 +45,7 @@ OFILES=\
 	5obj.$O\
 	6obj.$O\
 	8obj.$O\
-	$(GOOS).$O\
+	$(shell uname | tr A-Z a-z).$O\
 
 HFILES=$(GOROOT)/include/mach.h elf.h macho.h obj.h