diff --git a/app/logical/post_query_builder.rb b/app/logical/post_query_builder.rb
index 314d5b18a..7ef9a5318 100644
--- a/app/logical/post_query_builder.rb
+++ b/app/logical/post_query_builder.rb
@@ -195,30 +195,19 @@ class PostQueryBuilder
       relation = relation.where.not("posts.file_ext": q[:filetype_neg])
     end
 
-    # The SourcePattern SQL function replaces Pixiv sources with "pixiv/[suffix]", where
-    # [suffix] is everything past the second-to-last slash in the URL.  It leaves non-Pixiv
-    # URLs unchanged.  This is to ease database load for Pixiv source searches.
     if q[:source]
-      if q[:source] == "none%"
+      if q[:source] == "none"
         relation = relation.where("posts.source = ''")
-      elsif q[:source] == "http%"
-        relation = relation.where("(lower(posts.source) like ?)", "http%")
-      elsif q[:source] =~ /^(?:https?:\/\/)?%\.?pixiv(?:\.net(?:\/img)?)?(?:%\/img\/|%\/|(?=%$))(.+)$/i
-        relation = relation.where("SourcePattern(lower(posts.source)) LIKE lower(?) ESCAPE E'\\\\'", "pixiv/" + $1)
       else
-        relation = relation.where("SourcePattern(lower(posts.source)) LIKE SourcePattern(lower(?)) ESCAPE E'\\\\'", q[:source])
+        relation = relation.where_ilike(:source, q[:source].downcase + "*")
       end
     end
 
     if q[:source_neg]
-      if q[:source_neg] == "none%"
+      if q[:source_neg] == "none"
         relation = relation.where("posts.source != ''")
-      elsif q[:source_neg] == "http%"
-        relation = relation.where("(lower(posts.source) not like ?)", "http%")
-      elsif q[:source_neg] =~ /^(?:https?:\/\/)?%\.?pixiv(?:\.net(?:\/img)?)?(?:%\/img\/|%\/|(?=%$))(.+)$/i
-        relation = relation.where("SourcePattern(lower(posts.source)) NOT LIKE lower(?) ESCAPE E'\\\\'", "pixiv/" + $1)
       else
-        relation = relation.where("SourcePattern(lower(posts.source)) NOT LIKE SourcePattern(lower(?)) ESCAPE E'\\\\'", q[:source_neg])
+        relation = relation.where_not_ilike(:source, q[:source_neg].downcase + "*")
       end
     end
 
diff --git a/app/models/tag.rb b/app/models/tag.rb
index 2463b8488..503c5ee19 100644
--- a/app/models/tag.rb
+++ b/app/models/tag.rb
@@ -751,12 +751,10 @@ class Tag < ApplicationRecord
             q[:filesize] = parse_helper_fudged(g2, :filesize)
 
           when "source"
-            src = g2.gsub(/\A"(.*)"\Z/, '\1')
-            q[:source] = (src.to_escaped_for_sql_like + "%").gsub(/%+/, '%')
+            q[:source] = g2.gsub(/\A"(.*)"\Z/, '\1')
 
           when "-source"
-            src = g2.gsub(/\A"(.*)"\Z/, '\1')
-            q[:source_neg] = (src.to_escaped_for_sql_like + "%").gsub(/%+/, '%')
+            q[:source_neg] = g2.gsub(/\A"(.*)"\Z/, '\1')
 
           when "date"
             q[:date] = parse_helper(g2, :date)
diff --git a/db/migrate/20190829055758_drop_source_pattern_index_on_posts.rb b/db/migrate/20190829055758_drop_source_pattern_index_on_posts.rb
new file mode 100644
index 000000000..e36b05629
--- /dev/null
+++ b/db/migrate/20190829055758_drop_source_pattern_index_on_posts.rb
@@ -0,0 +1,24 @@
+# see db/migrate/20130328092739_change_source_pattern_index_on_posts.rb
+
+class DropSourcePatternIndexOnPosts < ActiveRecord::Migration[6.0]
+  def up
+    execute "set statement_timeout = 0"
+
+    execute "DROP INDEX index_posts_on_source_pattern"
+    execute "DROP FUNCTION SourcePattern(text)"
+    add_index :posts, "lower(source) gin_trgm_ops", name: "index_posts_on_source_trgm", using: :gin, where: "source != ''"
+  end
+
+  def down
+    execute "set statement_timeout = 0"
+
+    remove_index :posts, name: "index_posts_on_source_trgm"
+    execute "CREATE FUNCTION SourcePattern(src text) RETURNS text AS $$
+               BEGIN
+                 RETURN regexp_replace(src, '^[^/]*(//)?[^/]*\.pixiv\.net/img.*(/[^/]*/[^/]*)$', E'pixiv\\\\2');
+               END;
+             $$ LANGUAGE plpgsql IMMUTABLE RETURNS NULL ON NULL INPUT"
+    execute "CREATE INDEX index_posts_on_source_pattern ON posts USING btree
+             ((SourcePattern(source)) text_pattern_ops)"
+  end
+end
diff --git a/db/structure.sql b/db/structure.sql
index fc403b707..83556d72c 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -336,19 +336,6 @@ CREATE FUNCTION public.favorites_insert_trigger() RETURNS trigger
       $$;
 
 
---
--- Name: sourcepattern(text); Type: FUNCTION; Schema: public; Owner: -
---
-
-CREATE FUNCTION public.sourcepattern(src text) RETURNS text
-    LANGUAGE plpgsql IMMUTABLE STRICT
-    AS $_$
-               BEGIN
-                 RETURN regexp_replace(src, '^[^/]*(//)?[^/]*.pixiv.net/img.*(/[^/]*/[^/]*)$', E'pixiv\\2');
-               END;
-             $_$;
-
-
 --
 -- Name: testprs_end(internal); Type: FUNCTION; Schema: public; Owner: -
 --
@@ -6779,10 +6766,10 @@ CREATE INDEX index_posts_on_pixiv_id ON public.posts USING btree (pixiv_id) WHER
 
 
 --
--- Name: index_posts_on_source_pattern; Type: INDEX; Schema: public; Owner: -
+-- Name: index_posts_on_source_trgm; Type: INDEX; Schema: public; Owner: -
 --
 
-CREATE INDEX index_posts_on_source_pattern ON public.posts USING btree (public.sourcepattern(lower((source)::text)) text_pattern_ops);
+CREATE INDEX index_posts_on_source_trgm ON public.posts USING gin (lower((source)::text) public.gin_trgm_ops) WHERE ((source)::text <> ''::text);
 
 
 --
@@ -7327,6 +7314,7 @@ INSERT INTO "schema_migrations" (version) VALUES
 ('20190827233235'),
 ('20190827234625'),
 ('20190828005453'),
-('20190829052629');
+('20190829052629'),
+('20190829055758');
 
 
diff --git a/test/unit/post_test.rb b/test/unit/post_test.rb
index 209b8e045..061ab978d 100644
--- a/test/unit/post_test.rb
+++ b/test/unit/post_test.rb
@@ -2206,8 +2206,6 @@ class PostTest < ActiveSupport::TestCase
       assert_tag_match([],     "source:*.pixiv.net/img*/artist-fake/*")
       assert_tag_match([post], "source:http://*.pixiv.net/img*/img/artist-name/*")
       assert_tag_match([],     "source:http://*.pixiv.net/img*/img/artist-fake/*")
-      assert_tag_match([post], "source:pixiv/artist-name/*")
-      assert_tag_match([],     "source:pixiv/artist-fake/*")
     end
 
     should "return posts for a pixiv id search (type 1)" do