diff --git a/src/backend/commands/collationcmds.c b/src/backend/commands/collationcmds.c
new file mode 100644
index ebb0994..40e2626
--- a/src/backend/commands/collationcmds.c
+++ b/src/backend/commands/collationcmds.c
@@ -86,19 +86,47 @@ DefineCollation(ParseState *pstate, List
 		DefElem   **defelp;
 
 		if (strcmp(defel->defname, "from") == 0)
+		{
+			if (fromEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &fromEl;
+		}
 		else if (strcmp(defel->defname, "locale") == 0)
+		{
+			if (localeEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &localeEl;
+		}
 		else if (strcmp(defel->defname, "lc_collate") == 0)
+		{
+			if (lccollateEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &lccollateEl;
+		}
 		else if (strcmp(defel->defname, "lc_ctype") == 0)
+		{
+			if (lcctypeEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &lcctypeEl;
+		}
 		else if (strcmp(defel->defname, "provider") == 0)
+		{
+			if (providerEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &providerEl;
+		}
 		else if (strcmp(defel->defname, "deterministic") == 0)
+		{
+			if (deterministicEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &deterministicEl;
+		}
 		else if (strcmp(defel->defname, "version") == 0)
+		{
+			if (versionEl)
+				errorDuplicateDefElem(defel, pstate);
 			defelp = &versionEl;
+		}
 		else
 		{
 			ereport(ERROR,
@@ -112,11 +140,17 @@ DefineCollation(ParseState *pstate, List
 		*defelp = defel;
 	}
 
-	if ((localeEl && (lccollateEl || lcctypeEl))
-		|| (fromEl && list_length(parameters) != 1))
+	if (localeEl && (lccollateEl || lcctypeEl))
 		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("conflicting or redundant options")));
+				errcode(ERRCODE_SYNTAX_ERROR),
+				errmsg("conflicting or redundant options"),
+				errdetail("LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE."));
+
+	if (fromEl && list_length(parameters) != 1)
+		ereport(ERROR,
+				errcode(ERRCODE_SYNTAX_ERROR),
+				errmsg("conflicting or redundant options"),
+				errdetail("FROM cannot be specified together with any other options."));
 
 	if (fromEl)
 	{
diff --git a/src/backend/commands/define.c b/src/backend/commands/define.c
new file mode 100644
index aafd755..8dd260d
--- a/src/backend/commands/define.c
+++ b/src/backend/commands/define.c
@@ -359,3 +359,21 @@ errorConflictingDefElem(DefElem *defel,
 			errmsg("conflicting or redundant options"),
 			parser_errposition(pstate, defel->location));
 }
+
+/*
+ * Raise an error about a duplicate DefElem.
+ *
+ * This is similar to errorConflictingDefElem(), except that it is intended for
+ * an option that the user explicitly specified more than once.  This should
+ * only be used if defel->defname is guaranteed to match the user-entered
+ * option name, otherwise the detail text might be confusing.
+ */
+void
+errorDuplicateDefElem(DefElem *defel, ParseState *pstate)
+{
+	ereport(ERROR,
+			errcode(ERRCODE_SYNTAX_ERROR),
+			errmsg("conflicting or redundant options"),
+			errdetail("Option \"%s\" specified more than once.", defel->defname),
+			parser_errposition(pstate, defel->location));
+}
diff --git a/src/include/commands/defrem.h b/src/include/commands/defrem.h
new file mode 100644
index f84d099..91743ca
--- a/src/include/commands/defrem.h
+++ b/src/include/commands/defrem.h
@@ -154,5 +154,6 @@ extern TypeName *defGetTypeName(DefElem
 extern int	defGetTypeLength(DefElem *def);
 extern List *defGetStringList(DefElem *def);
 extern void errorConflictingDefElem(DefElem *defel, ParseState *pstate) pg_attribute_noreturn();
+extern void errorDuplicateDefElem(DefElem *defel, ParseState *pstate) pg_attribute_noreturn();
 
 #endif							/* DEFREM_H */
diff --git a/src/test/regress/expected/collate.out b/src/test/regress/expected/collate.out
new file mode 100644
index 0b60b55..c08d8f2
--- a/src/test/regress/expected/collate.out
+++ b/src/test/regress/expected/collate.out
@@ -701,6 +701,65 @@ View definition:
  SELECT ss.c1 + 1 AS c1p
    FROM ( SELECT 4 AS c1) ss;
 
+-- Check conflicting or duplicate options in CREATE COLLATION
+-- FROM
+CREATE COLLATION coll_dup_chk (FROM = "C", FROM = "X");
+ERROR:  conflicting or redundant options
+LINE 1: CREATE COLLATION coll_dup_chk (FROM = "C", FROM = "X");
+                                                   ^
+DETAIL:  Option "from" specified more than once.
+-- FROM conflicts with any other option
+CREATE COLLATION coll_dup_chk (FROM = "C", VERSION = "1");
+ERROR:  conflicting or redundant options
+DETAIL:  FROM cannot be specified together with any other options.
+-- LC_COLLATE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LC_COLLATE = "NONSENSE", LC_CTYPE = "POSIX");
+ERROR:  conflicting or redundant options
+LINE 1: ...ATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LC_COLLATE...
+                                                             ^
+DETAIL:  Option "lc_collate" specified more than once.
+-- LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_CTYPE = "POSIX", LC_CTYPE = "NONSENSE", LC_COLLATE = "POSIX");
+ERROR:  conflicting or redundant options
+LINE 1: ...REATE COLLATION coll_dup_chk (LC_CTYPE = "POSIX", LC_CTYPE =...
+                                                             ^
+DETAIL:  Option "lc_ctype" specified more than once.
+-- PROVIDER
+CREATE COLLATION coll_dup_chk (PROVIDER = icu, PROVIDER = NONSENSE, LC_COLLATE = "POSIX", LC_CTYPE = "POSIX");
+ERROR:  conflicting or redundant options
+LINE 1: CREATE COLLATION coll_dup_chk (PROVIDER = icu, PROVIDER = NO...
+                                                       ^
+DETAIL:  Option "provider" specified more than once.
+-- LOCALE
+CREATE COLLATION case_sensitive (LOCALE = '', LOCALE = "NONSENSE");
+ERROR:  conflicting or redundant options
+LINE 1: CREATE COLLATION case_sensitive (LOCALE = '', LOCALE = "NONS...
+                                                      ^
+DETAIL:  Option "locale" specified more than once.
+-- DETERMINISTIC
+CREATE COLLATION coll_dup_chk (DETERMINISTIC = TRUE, DETERMINISTIC = NONSENSE, LOCALE = '');
+ERROR:  conflicting or redundant options
+LINE 1: ...ATE COLLATION coll_dup_chk (DETERMINISTIC = TRUE, DETERMINIS...
+                                                             ^
+DETAIL:  Option "deterministic" specified more than once.
+-- VERSION
+CREATE COLLATION coll_dup_chk (VERSION = '1', VERSION = "NONSENSE", LOCALE = '');
+ERROR:  conflicting or redundant options
+LINE 1: CREATE COLLATION coll_dup_chk (VERSION = '1', VERSION = "NON...
+                                                      ^
+DETAIL:  Option "version" specified more than once.
+-- LOCALE conflicts with LC_COLLATE and LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LC_CTYPE = "POSIX", LOCALE = '');
+ERROR:  conflicting or redundant options
+DETAIL:  LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.
+-- LOCALE conflicts with LC_COLLATE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LOCALE = '');
+ERROR:  conflicting or redundant options
+DETAIL:  LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.
+-- LOCALE conflicts with LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_CTYPE = "POSIX", LOCALE = '');
+ERROR:  conflicting or redundant options
+DETAIL:  LOCALE cannot be specified together with LC_COLLATE or LC_CTYPE.
 --
 -- Clean up.  Many of these table names will be re-used if the user is
 -- trying to run any platform-specific collation tests later, so we
diff --git a/src/test/regress/sql/collate.sql b/src/test/regress/sql/collate.sql
new file mode 100644
index 30f811b..87c31d4
--- a/src/test/regress/sql/collate.sql
+++ b/src/test/regress/sql/collate.sql
@@ -272,6 +272,29 @@ SELECT c1+1 AS c1p FROM
   (SELECT ('4' COLLATE "C")::INT AS c1) ss;
 \d+ collate_on_int
 
+-- Check conflicting or duplicate options in CREATE COLLATION
+-- FROM
+CREATE COLLATION coll_dup_chk (FROM = "C", FROM = "X");
+-- FROM conflicts with any other option
+CREATE COLLATION coll_dup_chk (FROM = "C", VERSION = "1");
+-- LC_COLLATE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LC_COLLATE = "NONSENSE", LC_CTYPE = "POSIX");
+-- LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_CTYPE = "POSIX", LC_CTYPE = "NONSENSE", LC_COLLATE = "POSIX");
+-- PROVIDER
+CREATE COLLATION coll_dup_chk (PROVIDER = icu, PROVIDER = NONSENSE, LC_COLLATE = "POSIX", LC_CTYPE = "POSIX");
+-- LOCALE
+CREATE COLLATION case_sensitive (LOCALE = '', LOCALE = "NONSENSE");
+-- DETERMINISTIC
+CREATE COLLATION coll_dup_chk (DETERMINISTIC = TRUE, DETERMINISTIC = NONSENSE, LOCALE = '');
+-- VERSION
+CREATE COLLATION coll_dup_chk (VERSION = '1', VERSION = "NONSENSE", LOCALE = '');
+-- LOCALE conflicts with LC_COLLATE and LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LC_CTYPE = "POSIX", LOCALE = '');
+-- LOCALE conflicts with LC_COLLATE
+CREATE COLLATION coll_dup_chk (LC_COLLATE = "POSIX", LOCALE = '');
+-- LOCALE conflicts with LC_CTYPE
+CREATE COLLATION coll_dup_chk (LC_CTYPE = "POSIX", LOCALE = '');
 
 --
 -- Clean up.  Many of these table names will be re-used if the user is