diff --git a/arrow/compute/internal/kernels/scalar_set_lookup.go b/arrow/compute/internal/kernels/scalar_set_lookup.go
index fe9841ac..7b1caeb7 100644
--- a/arrow/compute/internal/kernels/scalar_set_lookup.go
+++ b/arrow/compute/internal/kernels/scalar_set_lookup.go
@@ -169,6 +169,25 @@ func (s *SetLookupState[T]) Init(opts SetLookupOptions) error {
 	if memoType == arrow.EXTENSION {
 		memoType = s.ValueSetType.(arrow.ExtensionType).StorageType().ID()
 	}
+	// FixedSizeBinary with byte-widths 1/2/4/8 takes the numeric fast-path
+	// in CreateSetLookupState (SetLookupState[uintN] + visitNumeric[uintN]),
+	// so the lookup table must be the matching TypedMemoTable[uintN], not
+	// the BinaryMemoTable that newMemoTable would otherwise return for
+	// FIXED_SIZE_BINARY.
+	if memoType == arrow.FIXED_SIZE_BINARY {
+		if fsb, ok := s.ValueSetType.(*arrow.FixedSizeBinaryType); ok {
+			switch fsb.ByteWidth {
+			case 1:
+				memoType = arrow.UINT8
+			case 2:
+				memoType = arrow.UINT16
+			case 4:
+				memoType = arrow.UINT32
+			case 8:
+				memoType = arrow.UINT64
+			}
+		}
+	}
 	lookup, err := newMemoTable(s.Alloc, memoType)
 	if err != nil {
 		return err
diff --git a/arrow/compute/scalar_set_lookup.go b/arrow/compute/scalar_set_lookup.go
index 84305536..9323fc0a 100644
--- a/arrow/compute/scalar_set_lookup.go
+++ b/arrow/compute/scalar_set_lookup.go
@@ -207,8 +207,14 @@ func RegisterScalarSetLookup(reg FunctionRegistry) {
 		kn.MemAlloc = exec.MemPrealloc
 		kn.NullHandling = exec.NullComputedPrealloc
 		kn.CleanupFn = func(state exec.KernelState) error {
-			s := state.(*kernels.SetLookupState[[]byte])
-			s.Lookup.(*hashing.BinaryMemoTable).Release()
+			// FixedSizeBinary widths 1/2/4/8 use SetLookupState[uintN] +
+			// the matching numeric memo table, which carries no buffers
+			// to release. Only the BinaryMemoTable path needs cleanup.
+			if s, ok := state.(*kernels.SetLookupState[[]byte]); ok {
+				if memo, ok := s.Lookup.(*hashing.BinaryMemoTable); ok {
+					memo.Release()
+				}
+			}
 			return nil
 		}
 
diff --git a/arrow/compute/scalar_set_lookup_test.go b/arrow/compute/scalar_set_lookup_test.go
index b28c3d75..010bb52c 100644
--- a/arrow/compute/scalar_set_lookup_test.go
+++ b/arrow/compute/scalar_set_lookup_test.go
@@ -18,6 +18,7 @@ package compute_test
 
 import (
 	"context"
+	"encoding/base64"
 	"fmt"
 	"strings"
 	"sync"
@@ -265,6 +266,37 @@ func (ss *ScalarSetLookupSuite) TestIsInFixedSizeBinary() {
 	}
 }
 
+func (ss *ScalarSetLookupSuite) TestIsInFixedSizeBinaryFastPaths() {
+	// ByteWidths 1, 2, 4, 8 take the SetLookupState[uintN] / visitNumeric
+	// fast-path. Before the fix in #785 this panicked because Init asked
+	// newMemoTable for a FIXED_SIZE_BINARY table (BinaryMemoTable) but the
+	// state expected a TypedMemoTable[uintN]; afterwards the cleanup hook
+	// also tried to type-assert all states as SetLookupState[[]byte].
+	pad := func(s string, w int) string {
+		buf := make([]byte, w)
+		copy(buf, s)
+		return string(buf)
+	}
+	enc := func(s string) string {
+		// scalar_set_lookup_test uses base64-encoded JSON entries via
+		// FixedSizeBinary's standard JSON shape; the helpers below
+		// already accept JSON arrays of base64 strings.
+		return base64.StdEncoding.EncodeToString([]byte(s))
+	}
+	for _, w := range []int{1, 2, 4, 8} {
+		w := w
+		ss.Run(fmt.Sprintf("ByteWidth=%d", w), func() {
+			typ := &arrow.FixedSizeBinaryType{ByteWidth: w}
+			input := fmt.Sprintf(`[%q, %q, %q]`,
+				enc(pad("a", w)), enc(pad("z", w)), enc(pad("b", w)))
+			valueset := fmt.Sprintf(`[%q, %q]`,
+				enc(pad("a", w)), enc(pad("b", w)))
+			ss.checkIsInFromJSON(typ, input, valueset,
+				`[true, false, true]`, compute.NullMatchingMatch)
+		})
+	}
+}
+
 func (ss *ScalarSetLookupSuite) TestIsInDecimal() {
 	type testCase struct {
 		expected string