diff --git a/doc/Makefile b/doc/Makefile
index bb8f551ad..bfdf0cce3 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -46,7 +46,6 @@ clean:
 	$(RM) -r ../html ../info
 
 install:
-	$(if $(PREFIX),,$(error variable "PREFIX" must be set))
 ifeq ($(wildcard ../html),../html)
 	$(INSTALL) -d $(DESTDIR)$(htmldir)
 	$(INSTALL) -m0644 ../html/*.* $(DESTDIR)$(htmldir)
diff --git a/libsrc/Makefile b/libsrc/Makefile
index 177314bdf..2018de801 100644
--- a/libsrc/Makefile
+++ b/libsrc/Makefile
@@ -96,7 +96,6 @@ INSTALL = install
 
 define INSTALL_recipe
 
-$(if $(PREFIX),,$(error variable "PREFIX" must be set))
 $(INSTALL) -d $(DESTDIR)$(datadir)/$(dir)
 $(INSTALL) -m0644 ../$(dir)/*.* $(DESTDIR)$(datadir)/$(dir)
 
diff --git a/samples/Makefile b/samples/Makefile
index 9732cfac7..01ad6f983 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -525,7 +525,6 @@ INSTALL = install
 samplesdir = $(PREFIX)/share/cc65/samples
 
 install:
-	$(if $(PREFIX),,$(error variable "PREFIX" must be set))
 	$(INSTALL) -d $(DESTDIR)$(samplesdir)
 	$(INSTALL) -d $(DESTDIR)$(samplesdir)/geos
 	$(INSTALL) -d $(DESTDIR)$(samplesdir)/tutorial
diff --git a/src/Makefile b/src/Makefile
index 75b92394e..8356d0001 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -26,7 +26,7 @@ PROGS = ar65     \
 .SUFFIXES:
 
 bindir  := $(PREFIX)/bin
-datadir := $(if $(PREFIX),$(PREFIX)/share/cc65,$(abspath ..))
+datadir := $(PREFIX)/share/cc65
 
 CA65_INC = $(datadir)/asminc
 CC65_INC = $(datadir)/include
@@ -111,7 +111,6 @@ $(RM) /usr/local/bin/$(prog)
 endef # UNAVAIL_recipe
 
 install:
-	$(if $(PREFIX),,$(error variable "PREFIX" must be set))
 	$(INSTALL) -d $(DESTDIR)$(bindir)
 	$(INSTALL) ../bin/* $(DESTDIR)$(bindir)