diff --git a/modules/db/test/blaze/db/api_test.clj b/modules/db/test/blaze/db/api_test.clj
index 094bd7e0c..f94274454 100644
--- a/modules/db/test/blaze/db/api_test.clj
+++ b/modules/db/test/blaze/db/api_test.clj
@@ -2239,6 +2239,38 @@
           count := 1
           [0 :id] := "0"))))
 
+  (testing "Medication"
+    (testing "with one ingredient reference"
+      (with-system-data [{:blaze.db/keys [node]} config]
+        [[[:put {:fhir/type :fhir/Medication :id "0"
+                 :ingredient
+                 [{:fhir/type :fhir.Medication/ingredient
+                   :item #fhir/Reference{:reference "Substance/0"}}]}]
+          [:put {:fhir/type :fhir/Substance :id "0"}]
+          [:put {:fhir/type :fhir/Medication :id "1"}]]]
+
+        (testing "ingredient"
+          (given (pull-type-query node "Medication" [["ingredient" "Substance/0"]])
+            count := 1
+            [0 :id] := "0"))))
+
+    (testing "with two ingredient references"
+      (with-system-data [{:blaze.db/keys [node]} config]
+        [[[:put {:fhir/type :fhir/Medication :id "0"
+                 :ingredient
+                 [{:fhir/type :fhir.Medication/ingredient
+                   :item #fhir/Reference{:reference "Substance/0"}}
+                  {:fhir/type :fhir.Medication/ingredient
+                   :item #fhir/Reference{:reference "Substance/1"}}]}]
+          [:put {:fhir/type :fhir/Substance :id "0"}]
+          [:put {:fhir/type :fhir/Substance :id "1"}]
+          [:put {:fhir/type :fhir/Medication :id "1"}]]]
+
+        (testing "ingredient"
+          (given (pull-type-query node "Medication" [["ingredient" "Substance/0"]])
+            count := 1
+            [0 :id] := "0")))))
+
   (testing "Observation"
     (with-system-data [{:blaze.db/keys [node]} config]
       [[[:put {:fhir/type :fhir/Observation :id "id-0"
diff --git a/modules/fhir-path/src/blaze/fhir_path.clj b/modules/fhir-path/src/blaze/fhir_path.clj
index 9add4a57c..270ce13ae 100644
--- a/modules/fhir-path/src/blaze/fhir_path.clj
+++ b/modules/fhir-path/src/blaze/fhir_path.clj
@@ -172,22 +172,21 @@
 
         (throw-anom (ba/incorrect (is-type-specifier-msg coll)))))))
 
-(defn- as-type-specifier-msg [coll]
-  (format "as type specifier with more than one item at the left side `%s`"
-          (pr-str coll)))
-
 (deftype AsTypeExpression [expression type-specifier]
   Expression
   (-eval [_ context coll]
     (let [coll (-eval expression context coll)]
       (case (coll/count coll)
-        0 coll
+        0 []
 
         1 (if (identical? type-specifier (fhir-spec/fhir-type (coll/nth coll 0)))
             coll
             [])
 
-        (throw-anom (ba/incorrect (as-type-specifier-msg coll)))))))
+        ;; HACK: normally multiple items should throw an error. However in R4 many
+        ;; FHIRPath expressions of search parameters use the as type specifier wrongly.
+        ;; Please remove that hack for R5.
+        (filterv #(identical? type-specifier (fhir-spec/fhir-type %)) coll)))))
 
 (deftype UnionExpression [e1 e2]
   Expression
@@ -260,7 +259,10 @@
           coll
           [])
 
-      (throw-anom (ba/incorrect (as-type-specifier-msg coll))))))
+      ;; HACK: normally multiple items should throw an error. However in R4 many
+      ;; FHIRPath expressions of search parameters use the as type specifier wrongly.
+      ;; Please remove that hack for R5.
+      (filterv #(identical? type-specifier (fhir-spec/fhir-type %)) coll))))
 
 (deftype OfTypeFunctionExpression [type-specifier]
   Expression
diff --git a/modules/fhir-path/test/blaze/fhir_path_test.clj b/modules/fhir-path/test/blaze/fhir_path_test.clj
index b74994d8d..d0b454ae8 100644
--- a/modules/fhir-path/test/blaze/fhir_path_test.clj
+++ b/modules/fhir-path/test/blaze/fhir_path_test.clj
@@ -18,7 +18,7 @@
    [taoensso.timbre :as log]))
 
 (st/instrument)
-(log/set-level! :trace)
+(log/set-min-level! :trace)
 
 (test/use-fixtures :each tu/fixture)
 
@@ -506,15 +506,19 @@
             {:fhir/type :fhir/Patient :id "foo"})
       count := 0))
 
-  (testing "multiple item returns an error"
+  ;; HACK: normally multiple items should throw an error. However in R4 many
+  ;; FHIRPath expressions of search parameters use the as type specifier wrongly.
+  ;; Please remove that hack for R5.
+  (testing "multiple items are filtered"
     (given (eval
-            "Patient.identifier as string"
+            "Patient.identifier as Identifier"
             {:fhir/type :fhir/Patient :id "id-162953"
              :identifier
              [#fhir/Identifier{:value "value-163922"}
               #fhir/Identifier{:value "value-163928"}]})
-      ::anom/category := ::anom/incorrect
-      ::anom/message := "as type specifier with more than one item at the left side `[#fhir/Identifier{:value \"value-163922\"} #fhir/Identifier{:value \"value-163928\"}]`")))
+      count := 2
+      [0] := #fhir/Identifier{:value "value-163922"}
+      [1] := #fhir/Identifier{:value "value-163928"})))
 
 ;; 6.3.4 as(type : type specifier)
 (deftest as-function-test
@@ -538,15 +542,19 @@
             {:fhir/type :fhir/Patient :id "foo"})
       count := 0))
 
-  (testing "multiple item returns an error"
+  ;; HACK: normally multiple items should throw an error. However in R4 many
+  ;; FHIRPath expressions of search parameters use the as type specifier wrongly.
+  ;; Please remove that hack for R5.
+  (testing "multiple items are filtered"
     (given (eval
-            "Patient.identifier.as(string)"
+            "Patient.identifier.as(Identifier)"
             {:fhir/type :fhir/Patient :id "id-162953"
              :identifier
              [#fhir/Identifier{:value "value-163922"}
               #fhir/Identifier{:value "value-163928"}]})
-      ::anom/category := ::anom/incorrect
-      ::anom/message := "as type specifier with more than one item at the left side `[#fhir/Identifier{:value \"value-163922\"} #fhir/Identifier{:value \"value-163928\"}]`")))
+      count := 2
+      [0] := #fhir/Identifier{:value "value-163922"}
+      [1] := #fhir/Identifier{:value "value-163928"})))
 
 ;; 6.5. Boolean logic