diff --git a/src/jolt/core.janet b/src/jolt/core.janet
index 0f04153..64dd89d 100644
--- a/src/jolt/core.janet
+++ b/src/jolt/core.janet
@@ -632,6 +632,13 @@
             (and (or (pvec? m) (tuple? m) (array? m))
                  (= 2 (if (pvec? m) (pv-count m) (length m))))
               (set result (core-assoc result (vnth m 0) (vnth m 1)))
+            # scalars, sets, and wrong-length sequentials can't merge into a map
+            # (a length-2 vector was handled above; anything else here is bad)
+            (or (number? m) (string? m) (buffer? m) (keyword? m) (boolean? m)
+                (set? m) (plist? m) (pvec? m) (tuple? m) (array? m)
+                (and (struct? m) (get m :jolt/type)))
+              (error (string "Can't merge " (type m) " into a map"))
+            # other map-like tables (records, sorted-maps, host tables): lenient conj
             (set result (core-conj result m))))
         (++ i))
       result)))
diff --git a/test/integration/clojure-test-suite-test.janet b/test/integration/clojure-test-suite-test.janet
index 1c79296..4d8b7e3 100644
--- a/test/integration/clojure-test-suite-test.janet
+++ b/test/integration/clojure-test-suite-test.janet
@@ -18,7 +18,7 @@
 
 # Baseline: assertions Jolt currently passes across the suite. Raise as Jolt
 # improves so a regression (previously-passing assertion breaking) is caught.
-(def baseline-pass 3870)
+(def baseline-pass 3875)
 # A file is "clean" when it ran with zero failures AND zero errors.
 (def baseline-clean-files 45)
 # Per-file wall-clock budget (seconds). Normal files finish in well under 1s;
diff --git a/test/spec/maps-spec.janet b/test/spec/maps-spec.janet
index c24dc3c..7f3ded5 100644
--- a/test/spec/maps-spec.janet
+++ b/test/spec/maps-spec.janet
@@ -90,4 +90,9 @@
   ["subvec out of range"     :throws "(subvec [0 1 2 3] 1 5)"]
   ["subvec start>end"        :throws "(subvec [0 1 2 3] 3 2)"]
   ["subvec ok"               "[1 2]" "(subvec [0 1 2 3] 1 3)"]
-  ["min-key empty"           :throws "(apply min-key identity [])"])
+  ["min-key empty"           :throws "(apply min-key identity [])"]
+  ["merge empty vector"      :throws "(merge {} [])"]
+  ["merge 1-elem vector"     :throws "(merge {} [:foo])"]
+  ["merge atomic arg"        :throws "(merge {} :foo)"]
+  ["merge [k v] ok"          "{:foo 1}" "(merge {} [:foo 1])"]
+  ["merge maps ok"           "{:a 1, :b 2}" "(merge {:a 1} {:b 2})"])