diff --git a/doc/Makefile b/doc/Makefile
index 96a3ba59b..33b5c2686 100644
--- a/doc/Makefile
+++ b/doc/Makefile
@@ -6,8 +6,8 @@ endif
 
 .SUFFIXES:
 
-htmldir = $(prefix)/share/doc/cc65$(DESTPACKAGE_SUFFIX)/html
-infodir = $(prefix)/share/info
+htmldir = $(PREFIX)/share/doc/cc65$(DESTPACKAGE_SUFFIX)/html
+infodir = $(PREFIX)/share/info
 
 ifdef CMD_EXE
 
@@ -46,7 +46,7 @@ clean:
 	$(RM) -r ../html ../info
 
 install:
-	$(if $(prefix),,$(error variable `prefix' must be set))
+	$(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 89d4b7752..0583b6761 100644
--- a/libsrc/Makefile
+++ b/libsrc/Makefile
@@ -72,7 +72,7 @@ endif
 
 ifndef TARGET
 
-datadir = $(prefix)/share/cc65
+datadir = $(PREFIX)/share/cc65
 
 all lib: $(TARGETS)
 
@@ -92,7 +92,7 @@ INSTALL = install
 
 define INSTALL_recipe
 
-$(if $(prefix),,$(error variable `prefix' must be set))
+$(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 949940022..59841d655 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -237,10 +237,10 @@ samples.atr: samples
 # Installation rules
 
 INSTALL = install
-samplesdir = $(prefix)/share/cc65
+samplesdir = $(PREFIX)/share/cc65/samples
 
 install:
-	$(if $(prefix),,$(error variable `prefix' must be set))
+	$(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 3ce4b676a..8b41ceb9c 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -19,8 +19,8 @@ PROGS = ar65     \
 
 .SUFFIXES:
 
-bindir  := $(prefix)/bin
-datadir := $(if $(prefix),$(prefix)/share/cc65,$(abspath ..))
+bindir  := $(PREFIX)/bin
+datadir := $(if $(PREFIX),$(PREFIX)/share/cc65,$(abspath ..))
 
 CA65_INC = $(datadir)/asminc
 CC65_INC = $(datadir)/include
@@ -107,7 +107,7 @@ $(RM) /usr/local/bin/$(prog)
 endef # UNAVAIL_recipe
 
 install:
-	$(if $(prefix),,$(error variable `prefix' must be set))
+	$(if $(PREFIX),,$(error variable `PREFIX' must be set))
 	$(INSTALL) -d $(DESTDIR)$(bindir)
 	$(INSTALL) ../bin/* $(DESTDIR)$(bindir)