diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 3841b9d6e2b..9796d0348d8 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,18 @@
 2001-12-16  Kaveh R. Ghazi  <ghazi@caip.rutgers.edu>
 
+	* i386/uwin.h (MD_STARTFILE_PREFIX): Avoid redefinition warnings.
+	* interix.h (TARGET_MEM_FUNCTIONS): Likewise.
+	* psos.h (CPP_PREDEFINES): Likewise.
+	* rs6000/linux64.h (ROUND_TYPE_ALIGN): Likewise.
+	* rs6000/xcoff.h (RS6000_MCOUNT, RS6000_ITRUNC, RS6000_UITRUNC,
+	ASM_OUTPUT_EXTERNAL): Likewise.
+	* sparc/liteelf.h (DWARF_DEBUGGING_INFO, DWARF2_DEBUGGING_INFO):
+	Likewise.
+	* sparc/sp64-elf.h (UNALIGNED_DOUBLE_INT_ASM_OP): Likewise.
+	* sparc/sp86x-elf.h (DWARF_DEBUGGING_INFO, DWARF2_DEBUGGING_INFO):
+	Likewise.
+	* sparc/sunos4.h (SUNOS4_SHARED_LIBRARIES): Likewise.
+
 	* c-lex.c (lex_number): Use ISXDIGIT/hex_value.
 	* vax/xm-vms.h (FILE_NAME_NONDIRECTORY): Use ISUPPER/TOLOWER.
 	* fold-const.c (real_hex_to_f): Use hex_value.
diff --git a/gcc/config/i386/uwin.h b/gcc/config/i386/uwin.h
index 7dd091c8c8e..ca39ffd9493 100644
--- a/gcc/config/i386/uwin.h
+++ b/gcc/config/i386/uwin.h
@@ -29,6 +29,7 @@ Boston, MA 02111-1307, USA.  */
 
 #define STANDARD_INCLUDE_COMPONENT "UWIN"
 #define SYSTEM_INCLUDE_DIR "/usr/gnu/include"
+#undef MD_STARTFILE_PREFIX
 #define MD_STARTFILE_PREFIX "/usr/gnu/lib/"
 
 #undef CPP_PREDEFINES
diff --git a/gcc/config/interix.h b/gcc/config/interix.h
index 054ce7d9487..0f203f3cf48 100644
--- a/gcc/config/interix.h
+++ b/gcc/config/interix.h
@@ -22,7 +22,9 @@ along with GNU CC; see the file COPYING.  If not, write to
 the Free Software Foundation, 59 Temple Place - Suite 330,
 Boston, MA 02111-1307, USA.  */
 
+#ifndef TARGET_MEM_FUNCTIONS
 #define TARGET_MEM_FUNCTIONS
+#endif
 
 /* POSIX/Uni-thread only for now.  Look at the winnt version
 for windows/multi thread */
diff --git a/gcc/config/psos.h b/gcc/config/psos.h
index 26be5ef8193..9529a216826 100644
--- a/gcc/config/psos.h
+++ b/gcc/config/psos.h
@@ -59,6 +59,7 @@ Boston, MA 02111-1307, USA.
 
 /* Predefined macros (independent of processor type). */
 
+#undef CPP_PREDEFINES
 #define CPP_PREDEFINES "-Dpsos"
 
 
diff --git a/gcc/config/rs6000/linux64.h b/gcc/config/rs6000/linux64.h
index ab04ba5d028..785ee88ebb0 100644
--- a/gcc/config/rs6000/linux64.h
+++ b/gcc/config/rs6000/linux64.h
@@ -41,6 +41,7 @@ Boston, MA 02111-1307, USA.  */
 
 /* AIX increases natural record alignment to doubleword if the first
    field is an FP double while the FP fields remain word aligned.  */
+#undef ROUND_TYPE_ALIGN
 #define ROUND_TYPE_ALIGN(STRUCT, COMPUTED, SPECIFIED)	\
   ((TREE_CODE (STRUCT) == RECORD_TYPE			\
     || TREE_CODE (STRUCT) == UNION_TYPE			\
diff --git a/gcc/config/rs6000/xcoff.h b/gcc/config/rs6000/xcoff.h
index 890ec4aee30..246e9d9d593 100644
--- a/gcc/config/rs6000/xcoff.h
+++ b/gcc/config/rs6000/xcoff.h
@@ -224,11 +224,14 @@ toc_section ()						\
 #define RESTORE_FP_SUFFIX ""
 
 /* Function name to call to do profiling.  */
+#undef RS6000_MCOUNT
 #define RS6000_MCOUNT ".__mcount"
 
 /* Function names to call to do floating point truncation.  */
 
+#undef RS6000_ITRUNC
 #define RS6000_ITRUNC "__itrunc"
+#undef RS6000_UITRUNC
 #define RS6000_UITRUNC "__uitrunc"
 
 /* This outputs NAME to FILE up to the first null or '['.  */
@@ -376,6 +379,7 @@ toc_section ()						\
 
 /* This says how to output an external.  */
 
+#undef ASM_OUTPUT_EXTERNAL
 #define ASM_OUTPUT_EXTERNAL(FILE, DECL, NAME)	\
 { rtx _symref = XEXP (DECL_RTL (DECL), 0);	\
   if ((TREE_CODE (DECL) == VAR_DECL		\
diff --git a/gcc/config/sparc/liteelf.h b/gcc/config/sparc/liteelf.h
index 1c4525c500f..d7c88b5c521 100644
--- a/gcc/config/sparc/liteelf.h
+++ b/gcc/config/sparc/liteelf.h
@@ -24,7 +24,9 @@ Boston, MA 02111-1307, USA.  */
 
 /* Default to dwarf2 in ELF.  */
 
+#undef DWARF_DEBUGGING_INFO
 #define DWARF_DEBUGGING_INFO
+#undef DWARF2_DEBUGGING_INFO
 #define DWARF2_DEBUGGING_INFO
 
 #undef PREFERRED_DEBUGGING_TYPE
diff --git a/gcc/config/sparc/sp64-elf.h b/gcc/config/sparc/sp64-elf.h
index 07be3885efb..40d18dfac97 100644
--- a/gcc/config/sparc/sp64-elf.h
+++ b/gcc/config/sparc/sp64-elf.h
@@ -117,4 +117,5 @@ crtbegin.o%s \
 
 /* Define the names of various pseudo-ops used by the Sparc/svr4 assembler.  */
 
+#undef UNALIGNED_DOUBLE_INT_ASM_OP
 #define UNALIGNED_DOUBLE_INT_ASM_OP	"\t.uaxword\t"
diff --git a/gcc/config/sparc/sp86x-elf.h b/gcc/config/sparc/sp86x-elf.h
index 5ae99e31e44..40ecd55ef4d 100644
--- a/gcc/config/sparc/sp86x-elf.h
+++ b/gcc/config/sparc/sp86x-elf.h
@@ -24,7 +24,9 @@ Boston, MA 02111-1307, USA.  */
 
 /* Default to dwarf2 in ELF.  */
 
+#undef DWARF_DEBUGGING_INFO
 #define DWARF_DEBUGGING_INFO
+#undef DWARF2_DEBUGGING_INFO
 #define DWARF2_DEBUGGING_INFO
 
 #undef PREFERRED_DEBUGGING_TYPE
diff --git a/gcc/config/sparc/sunos4.h b/gcc/config/sparc/sunos4.h
index e5ec1ee3a66..a6c11d9ff35 100644
--- a/gcc/config/sparc/sunos4.h
+++ b/gcc/config/sparc/sunos4.h
@@ -18,6 +18,7 @@ along with GNU CC; see the file COPYING.  If not, write to
 the Free Software Foundation, 59 Temple Place - Suite 330,
 Boston, MA 02111-1307, USA.  */
 
+#undef SUNOS4_SHARED_LIBRARIES
 #define SUNOS4_SHARED_LIBRARIES 1
 
 #undef CPP_PREDEFINES