diff --git a/intl/icu/source/acinclude.m4 b/intl/icu/source/acinclude.m4
--- a/intl/icu/source/acinclude.m4
+++ b/intl/icu/source/acinclude.m4
@@ -466,30 +466,36 @@ AC_DEFUN([AC_CHECK_STRICT_COMPILE],
             *)
                 # Do not use -ansi. It limits us to C90, and it breaks some platforms.
                 # We use -std=c99 to disable the gnu99 defaults and its associated warnings
                 CFLAGS="$CFLAGS -std=c99"
                 ;;
             esac
             
             CFLAGS="$CFLAGS -Wall -pedantic -Wshadow -Wpointer-arith -Wmissing-prototypes -Wwrite-strings"
+
+            # Suppress clang C warnings:
+            CFLAGS="$CFLAGS -Wno-sign-compare -Wno-unused"
         else
             case "${host}" in
             *-*-cygwin)
                 if test "`$CC /help 2>&1 | head -c9`" = "Microsoft"
                 then
                     CFLAGS="$CFLAGS /W4"
                 fi ;;
             *-*-mingw32|*-*-mingw64)
                 CFLAGS="$CFLAGS -W4" ;;
             esac
         fi
         if test "$GXX" = yes
         then
             CXXFLAGS="$CXXFLAGS -W -Wall -pedantic -Wpointer-arith -Wwrite-strings -Wno-long-long"
+
+            # Suppress clang C++ warnings:
+            CXXFLAGS="$CXXFLAGS -Wno-unused -Wno-unused-parameter"
         else
             case "${host}" in
             *-*-cygwin)
                 if test "`$CXX /help 2>&1 | head -c9`" = "Microsoft"
                 then
                     CXXFLAGS="$CXXFLAGS /W4"
                 fi ;;
             *-*-mingw32|*-*-mingw64)
diff --git a/intl/icu/source/configure b/intl/icu/source/configure
--- a/intl/icu/source/configure
+++ b/intl/icu/source/configure
@@ -4089,30 +4089,36 @@ fi
             *)
                 # Do not use -ansi. It limits us to C90, and it breaks some platforms.
                 # We use -std=c99 to disable the gnu99 defaults and its associated warnings
                 CFLAGS="$CFLAGS -std=c99"
                 ;;
             esac
 
             CFLAGS="$CFLAGS -Wall -pedantic -Wshadow -Wpointer-arith -Wmissing-prototypes -Wwrite-strings"
+
+            # Suppress clang C warnings:
+            CFLAGS="$CFLAGS -Wno-sign-compare -Wno-unused"
         else
             case "${host}" in
             *-*-cygwin)
                 if test "`$CC /help 2>&1 | head -c9`" = "Microsoft"
                 then
                     CFLAGS="$CFLAGS /W4"
                 fi ;;
             *-*-mingw32|*-*-mingw64)
                 CFLAGS="$CFLAGS -W4" ;;
             esac
         fi
         if test "$GXX" = yes
         then
             CXXFLAGS="$CXXFLAGS -W -Wall -pedantic -Wpointer-arith -Wwrite-strings -Wno-long-long"
+
+            # Suppress clang C++ warnings:
+            CXXFLAGS="$CXXFLAGS -Wno-unused -Wno-unused-parameter"
         else
             case "${host}" in
             *-*-cygwin)
                 if test "`$CXX /help 2>&1 | head -c9`" = "Microsoft"
                 then
                     CXXFLAGS="$CXXFLAGS /W4"
                 fi ;;
             *-*-mingw32|*-*-mingw64)