diff --git a/BasiliskII/src/Unix/Makefile.in b/BasiliskII/src/Unix/Makefile.in
index 6d04f350..42f1b049 100644
--- a/BasiliskII/src/Unix/Makefile.in
+++ b/BasiliskII/src/Unix/Makefile.in
@@ -21,7 +21,7 @@ CFLAGS = @CFLAGS@
 CXXFLAGS = @CXXFLAGS@
 CPUINCLUDES_FLAGS=@CPUINCLUDES@
 CPUINCLUDES_FLAGS:=$(CPUINCLUDES_FLAGS:-I%=-I@top_srcdir@/%)
-CPPFLAGS = @CPPFLAGS@ -I/opt/X11/include -I@top_srcdir@/../include -I@top_srcdir@/. -I. -I@top_srcdir@/../CrossPlatform $(CPUINCLUDES_FLAGS) -I@top_srcdir@/../slirp
+CPPFLAGS = @CPPFLAGS@ -I@top_srcdir@/../include -I@top_srcdir@/. -I. -I@top_srcdir@/../CrossPlatform $(CPUINCLUDES_FLAGS) -I@top_srcdir@/../slirp
 DEFS = @DEFS@ @DEFINES@ -D_REENTRANT -DDATADIR=\"$(datadir)/$(APP)\"
 LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@
diff --git a/SheepShaver/src/Unix/Makefile.in b/SheepShaver/src/Unix/Makefile.in
index f190e0ad..ed6148a4 100644
--- a/SheepShaver/src/Unix/Makefile.in
+++ b/SheepShaver/src/Unix/Makefile.in
@@ -17,7 +17,7 @@ CC = @CC@
 CXX = @CXX@
 CFLAGS = @CFLAGS@
 CXXFLAGS = @CXXFLAGS@
-CPPFLAGS = @CPPFLAGS@ -I/opt/X11/include -I../include -I. -I../CrossPlatform -I../slirp
+CPPFLAGS = @CPPFLAGS@ -I../include -I. -I../CrossPlatform -I../slirp
 DEFS = @DEFS@ -D_REENTRANT -DDATADIR=\"$(datadir)/$(APP)\"
 LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@