diff --git a/doc/src/sgml/ref/initdb.sgml b/doc/src/sgml/ref/initdb.sgml
index f01df2dde9..8158896298 100644
--- a/doc/src/sgml/ref/initdb.sgml
+++ b/doc/src/sgml/ref/initdb.sgml
@@ -209,8 +209,9 @@ PostgreSQL documentation
        <para>
         Selects the encoding of the template databases. This will also
         be the default encoding of any database you create later,
-        unless you override it then.  The default is derived from the locale, or
-        <literal>SQL_ASCII</literal> if that does not work. The character sets supported by
+        unless you override it then.  The default is derived from the locale,
+        if the libc locale provider is used, or <literal>UTF8</literal> if the
+        ICU locale provider is used.  The character sets supported by
         the <productname>PostgreSQL</productname> server are described
         in <xref linkend="multibyte-charset-supported"/>.
        </para>
diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index 6ff48bb18f..f248ad42b7 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -1034,6 +1034,12 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 
 	if (dblocprovider == COLLPROVIDER_ICU)
 	{
+		if (!(is_encoding_supported_by_icu(encoding)))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					 errmsg("encoding \"%s\" is not supported with ICU provider",
+							pg_encoding_to_char(encoding))));
+
 		/*
 		 * This would happen if template0 uses the libc provider but the new
 		 * database uses icu.
@@ -1042,10 +1048,9 @@ createdb(ParseState *pstate, const CreatedbStmt *stmt)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("ICU locale must be specified")));
-	}
 
-	if (dblocprovider == COLLPROVIDER_ICU)
 		check_icu_locale(dbiculocale);
+	}
 
 	/*
 	 * Check that the new encoding and locale settings match the source
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index 6aeec8d426..28f22b25b2 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -2042,6 +2042,27 @@ check_locale_encoding(const char *locale, int user_enc)
 	return true;
 }
 
+/*
+ * check if the chosen encoding matches is supported by ICU
+ *
+ * this should match the similar check in the backend createdb() function
+ */
+static bool
+check_icu_locale_encoding(int user_enc)
+{
+	if (!(is_encoding_supported_by_icu(user_enc)))
+	{
+		pg_log_error("encoding mismatch");
+		pg_log_error_detail("The encoding you selected (%s) is not supported with the ICU provider.",
+							pg_encoding_to_char(user_enc));
+		pg_log_error_hint("Rerun %s and either do not specify an encoding explicitly, "
+						  "or choose a matching combination.",
+						  progname);
+		return false;
+	}
+	return true;
+}
+
 /*
  * set up the locale variables
  *
@@ -2310,7 +2331,11 @@ setup_locale_encoding(void)
 	}
 
 	if (!encoding && locale_provider == COLLPROVIDER_ICU)
+	{
 		encodingid = PG_UTF8;
+		printf(_("The default database encoding has been set to \"%s\".\n"),
+			   pg_encoding_to_char(encodingid));
+	}
 	else if (!encoding)
 	{
 		int			ctype_enc;
@@ -2362,6 +2387,10 @@ setup_locale_encoding(void)
 	if (!check_locale_encoding(lc_ctype, encodingid) ||
 		!check_locale_encoding(lc_collate, encodingid))
 		exit(1);				/* check_locale_encoding printed the error */
+
+	if (locale_provider == COLLPROVIDER_ICU &&
+		!check_icu_locale_encoding(encodingid))
+		exit(1);
 }
 
 
diff --git a/src/bin/initdb/t/001_initdb.pl b/src/bin/initdb/t/001_initdb.pl
index a37f6dd9b3..164fc11cbf 100644
--- a/src/bin/initdb/t/001_initdb.pl
+++ b/src/bin/initdb/t/001_initdb.pl
@@ -118,6 +118,15 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		qr/FATAL:  could not open collator for locale/,
 		'fails for invalid ICU locale');
+
+	command_fails_like(
+		[
+			'initdb',                '--no-sync',
+			'--locale-provider=icu', '--encoding=SQL_ASCII',
+			'--icu-locale=en', "$tempdir/dataX"
+		],
+		qr/error: encoding mismatch/,
+		'fails for encoding not supported by ICU');
 }
 else
 {
diff --git a/src/bin/scripts/t/020_createdb.pl b/src/bin/scripts/t/020_createdb.pl
index e91c1d013d..e95f200d0b 100644
--- a/src/bin/scripts/t/020_createdb.pl
+++ b/src/bin/scripts/t/020_createdb.pl
@@ -50,6 +50,15 @@ if ($ENV{with_icu} eq 'yes')
 		],
 		'fails for invalid ICU locale');
 
+	$node->command_fails_like(
+		[
+			'createdb',             '-T',
+			'template0',            '--locale-provider=icu',
+			'--encoding=SQL_ASCII', 'foobarX'
+		],
+		qr/ERROR:  encoding "SQL_ASCII" is not supported with ICU provider/,
+		'fails for encoding not supported by ICU');
+
 	# additional node, which uses the icu provider
 	my $node2 = PostgreSQL::Test::Cluster->new('icu');
 	$node2->init(extra => ['--locale-provider=icu', '--icu-locale=en']);