diff --git a/internal/cmd/generate-types/impl.go b/internal/cmd/generate-types/impl.go
index 4b362c6..6068671 100644
--- a/internal/cmd/generate-types/impl.go
+++ b/internal/cmd/generate-types/impl.go
@@ -820,7 +820,7 @@
 	if oi := m.messageInfo().oneofs[od.Name()]; oi != nil && oi.oneofDesc == od {
 		return od.Fields().ByNumber(oi.which(m.pointer()))
 	}
-	panic("invalid oneof descriptor")
+	panic("invalid oneof descriptor " + string(od.FullName()) + " for message " + string(m.Descriptor().FullName()))
 }
 func (m *{{.}}) GetUnknown() protoreflect.RawFields {
 	m.messageInfo().init()
diff --git a/internal/filedesc/desc.go b/internal/filedesc/desc.go
index 13b7723..2540bef 100644
--- a/internal/filedesc/desc.go
+++ b/internal/filedesc/desc.go
@@ -607,7 +607,7 @@
 		// TODO: Avoid panic if we're running with the race detector
 		// and instead spawn a goroutine that periodically resets
 		// this value back to the original to induce a race.
-		panic("detected mutation on the default bytes")
+		panic(fmt.Sprintf("detected mutation on the default bytes for %v", fd.FullName()))
 	}
 	return dv.val
 }
diff --git a/internal/impl/message_reflect.go b/internal/impl/message_reflect.go
index 3eb2b13..0f4b8db 100644
--- a/internal/impl/message_reflect.go
+++ b/internal/impl/message_reflect.go
@@ -338,24 +338,27 @@
 	}
 	if fi != nil {
 		if fi.fieldDesc != fd {
-			panic("mismatching field descriptor")
+			if got, want := fd.FullName(), fi.fieldDesc.FullName(); got != want {
+				panic(fmt.Sprintf("mismatching field: got %v, want %v", got, want))
+			}
+			panic(fmt.Sprintf("mismatching field: %v", fd.FullName()))
 		}
 		return fi, nil
 	}
 
 	if fd.IsExtension() {
-		if fd.ContainingMessage().FullName() != mi.Desc.FullName() {
+		if got, want := fd.ContainingMessage().FullName(), mi.Desc.FullName(); got != want {
 			// TODO: Should this be exact containing message descriptor match?
-			panic("mismatching containing message")
+			panic(fmt.Sprintf("extension %v has mismatching containing message: got %v, want %v", fd.FullName(), got, want))
 		}
 		if !mi.Desc.ExtensionRanges().Has(fd.Number()) {
-			panic("invalid extension field")
+			panic(fmt.Sprintf("extension %v extends %v outside the extension range", fd.FullName(), mi.Desc.FullName()))
 		}
 		xtd, ok := fd.(pref.ExtensionTypeDescriptor)
 		if !ok {
-			panic("extension descriptor does not implement ExtensionTypeDescriptor")
+			panic(fmt.Sprintf("extension %v does not implement protoreflect.ExtensionTypeDescriptor", fd.FullName()))
 		}
 		return nil, xtd.Type()
 	}
-	panic("invalid field descriptor")
+	panic(fmt.Sprintf("field %v is invalid", fd.FullName()))
 }
diff --git a/internal/impl/message_reflect_field.go b/internal/impl/message_reflect_field.go
index ea6f755..23124a8 100644
--- a/internal/impl/message_reflect_field.go
+++ b/internal/impl/message_reflect_field.go
@@ -31,13 +31,13 @@
 func fieldInfoForOneof(fd pref.FieldDescriptor, fs reflect.StructField, x exporter, ot reflect.Type) fieldInfo {
 	ft := fs.Type
 	if ft.Kind() != reflect.Interface {
-		panic(fmt.Sprintf("invalid type: got %v, want interface kind", ft))
+		panic(fmt.Sprintf("field %v has invalid type: got %v, want interface kind", fd.FullName(), ft))
 	}
 	if ot.Kind() != reflect.Struct {
-		panic(fmt.Sprintf("invalid type: got %v, want struct kind", ot))
+		panic(fmt.Sprintf("field %v has invalid type: got %v, want struct kind", fd.FullName(), ot))
 	}
 	if !reflect.PtrTo(ot).Implements(ft) {
-		panic(fmt.Sprintf("invalid type: %v does not implement %v", ot, ft))
+		panic(fmt.Sprintf("field %v has invalid type: %v does not implement %v", fd.FullName(), ot, ft))
 	}
 	conv := NewConverter(ot.Field(0).Type, fd)
 	isMessage := fd.Message() != nil
@@ -90,7 +90,7 @@
 		},
 		mutable: func(p pointer) pref.Value {
 			if !isMessage {
-				panic("invalid Mutable on field with non-composite type")
+				panic(fmt.Sprintf("field %v with invalid Mutable call on field with non-composite type", fd.FullName()))
 			}
 			rv := p.Apply(fieldOffset).AsValueOf(fs.Type).Elem()
 			if rv.IsNil() || rv.Elem().Type().Elem() != ot || rv.Elem().IsNil() {
@@ -114,7 +114,7 @@
 func fieldInfoForMap(fd pref.FieldDescriptor, fs reflect.StructField, x exporter) fieldInfo {
 	ft := fs.Type
 	if ft.Kind() != reflect.Map {
-		panic(fmt.Sprintf("invalid type: got %v, want map kind", ft))
+		panic(fmt.Sprintf("field %v has invalid type: got %v, want map kind", fd.FullName(), ft))
 	}
 	conv := NewConverter(ft, fd)
 
@@ -147,7 +147,7 @@
 			rv := p.Apply(fieldOffset).AsValueOf(fs.Type).Elem()
 			pv := conv.GoValueOf(v)
 			if pv.IsNil() {
-				panic(fmt.Sprintf("invalid value: setting map field to read-only value"))
+				panic(fmt.Sprintf("map field %v cannot be set with read-only value", fd.FullName()))
 			}
 			rv.Set(pv)
 		},
@@ -167,7 +167,7 @@
 func fieldInfoForList(fd pref.FieldDescriptor, fs reflect.StructField, x exporter) fieldInfo {
 	ft := fs.Type
 	if ft.Kind() != reflect.Slice {
-		panic(fmt.Sprintf("invalid type: got %v, want slice kind", ft))
+		panic(fmt.Sprintf("field %v has invalid type: got %v, want slice kind", fd.FullName(), ft))
 	}
 	conv := NewConverter(reflect.PtrTo(ft), fd)
 
@@ -200,7 +200,7 @@
 			rv := p.Apply(fieldOffset).AsValueOf(fs.Type).Elem()
 			pv := conv.GoValueOf(v)
 			if pv.IsNil() {
-				panic(fmt.Sprintf("invalid value: setting repeated field to read-only value"))
+				panic(fmt.Sprintf("list field %v cannot be set with read-only value", fd.FullName()))
 			}
 			rv.Set(pv.Elem())
 		},
@@ -225,7 +225,7 @@
 	isBytes := ft.Kind() == reflect.Slice && ft.Elem().Kind() == reflect.Uint8
 	if nullable {
 		if ft.Kind() != reflect.Ptr && ft.Kind() != reflect.Slice {
-			panic(fmt.Sprintf("invalid type: got %v, want pointer", ft))
+			panic(fmt.Sprintf("field %v has invalid type: got %v, want pointer", fd.FullName(), ft))
 		}
 		if ft.Kind() == reflect.Ptr {
 			ft = ft.Elem()
@@ -257,7 +257,7 @@
 			case reflect.String, reflect.Slice:
 				return rv.Len() > 0
 			default:
-				panic(fmt.Sprintf("invalid type: %v", rv.Type())) // should never happen
+				panic(fmt.Sprintf("field %v has invalid type: %v", fd.FullName(), rv.Type())) // should never happen
 			}
 		},
 		clear: func(p pointer) {
@@ -314,7 +314,7 @@
 			messageName := fd.Message().FullName()
 			messageType, _ = preg.GlobalTypes.FindMessageByName(messageName)
 			if messageType == nil {
-				panic(fmt.Sprintf("weak message %v is not linked in", messageName))
+				panic(fmt.Sprintf("weak message %v for field %v is not linked in", messageName, fd.FullName()))
 			}
 		})
 	}
@@ -347,7 +347,10 @@
 			lazyInit()
 			m := v.Message()
 			if m.Descriptor() != messageType.Descriptor() {
-				panic("mismatching message descriptor")
+				if got, want := m.Descriptor().FullName(), messageType.Descriptor().FullName(); got != want {
+					panic(fmt.Sprintf("field %v has mismatching message descriptor: got %v, want %v", fd.FullName(), got, want))
+				}
+				panic(fmt.Sprintf("field %v has mismatching message descriptor: %v", fd.FullName(), m.Descriptor().FullName()))
 			}
 			p.Apply(weakOffset).WeakFields().set(num, m.Interface())
 		},
@@ -402,7 +405,7 @@
 			rv := p.Apply(fieldOffset).AsValueOf(fs.Type).Elem()
 			rv.Set(conv.GoValueOf(v))
 			if rv.IsNil() {
-				panic("invalid nil pointer")
+				panic(fmt.Sprintf("field %v has invalid nil pointer", fd.FullName()))
 			}
 		},
 		mutable: func(p pointer) pref.Value {
diff --git a/internal/impl/message_reflect_gen.go b/internal/impl/message_reflect_gen.go
index 7d65f5c..741d6e5 100644
--- a/internal/impl/message_reflect_gen.go
+++ b/internal/impl/message_reflect_gen.go
@@ -114,7 +114,7 @@
 	if oi := m.messageInfo().oneofs[od.Name()]; oi != nil && oi.oneofDesc == od {
 		return od.Fields().ByNumber(oi.which(m.pointer()))
 	}
-	panic("invalid oneof descriptor")
+	panic("invalid oneof descriptor " + string(od.FullName()) + " for message " + string(m.Descriptor().FullName()))
 }
 func (m *messageState) GetUnknown() protoreflect.RawFields {
 	m.messageInfo().init()
@@ -234,7 +234,7 @@
 	if oi := m.messageInfo().oneofs[od.Name()]; oi != nil && oi.oneofDesc == od {
 		return od.Fields().ByNumber(oi.which(m.pointer()))
 	}
-	panic("invalid oneof descriptor")
+	panic("invalid oneof descriptor " + string(od.FullName()) + " for message " + string(m.Descriptor().FullName()))
 }
 func (m *messageReflectWrapper) GetUnknown() protoreflect.RawFields {
 	m.messageInfo().init()
diff --git a/internal/impl/pointer_unsafe.go b/internal/impl/pointer_unsafe.go
index 2741643..088aa85 100644
--- a/internal/impl/pointer_unsafe.go
+++ b/internal/impl/pointer_unsafe.go
@@ -148,7 +148,11 @@
 	return pointer{p: unsafe.Pointer(ms)}
 }
 func (ms *messageState) messageInfo() *MessageInfo {
-	return ms.LoadMessageInfo()
+	mi := ms.LoadMessageInfo()
+	if mi == nil {
+		panic("invalid nil message info; this suggests memory corruption due to a race or shallow copy on the message struct")
+	}
+	return mi
 }
 func (ms *messageState) LoadMessageInfo() *MessageInfo {
 	return (*MessageInfo)(atomic.LoadPointer((*unsafe.Pointer)(unsafe.Pointer(&ms.atomicMessageInfo))))
diff --git a/proto/merge.go b/proto/merge.go
index 27ab1a6..d761ab3 100644
--- a/proto/merge.go
+++ b/proto/merge.go
@@ -5,6 +5,8 @@
 package proto
 
 import (
+	"fmt"
+
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/runtime/protoiface"
 )
@@ -26,6 +28,9 @@
 
 	dstMsg, srcMsg := dst.ProtoReflect(), src.ProtoReflect()
 	if dstMsg.Descriptor() != srcMsg.Descriptor() {
+		if got, want := dstMsg.Descriptor().FullName(), srcMsg.Descriptor().FullName(); got != want {
+			panic(fmt.Sprintf("descriptor mismatch: %v != %v", got, want))
+		}
 		panic("descriptor mismatch")
 	}
 	mergeOptions{}.mergeMessage(dstMsg, srcMsg)
@@ -72,7 +77,7 @@
 	}
 
 	if !dst.IsValid() {
-		panic("cannot merge into invalid destination message")
+		panic(fmt.Sprintf("cannot merge into invalid %v message", dst.Descriptor().FullName()))
 	}
 
 	src.Range(func(fd protoreflect.FieldDescriptor, v protoreflect.Value) bool {
diff --git a/proto/reset.go b/proto/reset.go
index 22048bc..3d7f894 100644
--- a/proto/reset.go
+++ b/proto/reset.go
@@ -4,7 +4,11 @@
 
 package proto
 
-import "google.golang.org/protobuf/reflect/protoreflect"
+import (
+	"fmt"
+
+	"google.golang.org/protobuf/reflect/protoreflect"
+)
 
 // Reset clears every field in the message.
 // The resulting message shares no observable memory with its previous state
@@ -19,7 +23,7 @@
 
 func resetMessage(m protoreflect.Message) {
 	if !m.IsValid() {
-		panic("cannot reset invalid message")
+		panic(fmt.Sprintf("cannot reset invalid %v message", m.Descriptor().FullName()))
 	}
 
 	// Clear all known fields.
diff --git a/reflect/protoreflect/value_union.go b/reflect/protoreflect/value_union.go
index d695a4d..f334f71 100644
--- a/reflect/protoreflect/value_union.go
+++ b/reflect/protoreflect/value_union.go
@@ -7,7 +7,6 @@
 import (
 	"fmt"
 	"math"
-	"reflect"
 )
 
 // Value is a union where only one Go type may be set at a time.
@@ -87,7 +86,7 @@
 	case Message, List, Map:
 		return valueOfIface(v)
 	default:
-		panic(fmt.Sprintf("invalid type: %v", reflect.TypeOf(v)))
+		panic(fmt.Sprintf("invalid type: %T", v))
 	}
 }
 
@@ -197,13 +196,55 @@
 	}
 }
 
+func (v Value) typeName() string {
+	switch v.typ {
+	case nilType:
+		return "nil"
+	case boolType:
+		return "bool"
+	case int32Type:
+		return "int32"
+	case int64Type:
+		return "int64"
+	case uint32Type:
+		return "uint32"
+	case uint64Type:
+		return "uint64"
+	case float32Type:
+		return "float32"
+	case float64Type:
+		return "float64"
+	case stringType:
+		return "string"
+	case bytesType:
+		return "bytes"
+	case enumType:
+		return "enum"
+	default:
+		switch v := v.getIface().(type) {
+		case Message:
+			return "message"
+		case List:
+			return "list"
+		case Map:
+			return "map"
+		default:
+			return fmt.Sprintf("<unknown: %T>", v)
+		}
+	}
+}
+
+func (v Value) panicMessage(what string) string {
+	return fmt.Sprintf("type mismatch: cannot convert %v to %s", v.typeName(), what)
+}
+
 // Bool returns v as a bool and panics if the type is not a bool.
 func (v Value) Bool() bool {
 	switch v.typ {
 	case boolType:
 		return v.num > 0
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("bool"))
 	}
 }
 
@@ -213,7 +254,7 @@
 	case int32Type, int64Type:
 		return int64(v.num)
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("int"))
 	}
 }
 
@@ -223,7 +264,7 @@
 	case uint32Type, uint64Type:
 		return uint64(v.num)
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("uint"))
 	}
 }
 
@@ -233,7 +274,7 @@
 	case float32Type, float64Type:
 		return math.Float64frombits(uint64(v.num))
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("float"))
 	}
 }
 
@@ -254,7 +295,7 @@
 	case bytesType:
 		return v.getBytes()
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("bytes"))
 	}
 }
 
@@ -264,37 +305,37 @@
 	case enumType:
 		return EnumNumber(v.num)
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("enum"))
 	}
 }
 
 // Message returns v as a Message and panics if the type is not a Message.
 func (v Value) Message() Message {
-	switch v := v.getIface().(type) {
+	switch vi := v.getIface().(type) {
 	case Message:
-		return v
+		return vi
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("message"))
 	}
 }
 
 // List returns v as a List and panics if the type is not a List.
 func (v Value) List() List {
-	switch v := v.getIface().(type) {
+	switch vi := v.getIface().(type) {
 	case List:
-		return v
+		return vi
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("list"))
 	}
 }
 
 // Map returns v as a Map and panics if the type is not a Map.
 func (v Value) Map() Map {
-	switch v := v.getIface().(type) {
+	switch vi := v.getIface().(type) {
 	case Map:
-		return v
+		return vi
 	default:
-		panic("proto: value type mismatch")
+		panic(v.panicMessage("map"))
 	}
 }
 
@@ -303,8 +344,9 @@
 	switch v.typ {
 	case boolType, int32Type, int64Type, uint32Type, uint64Type, stringType:
 		return MapKey(v)
+	default:
+		panic(v.panicMessage("map key"))
 	}
-	panic("proto: invalid map key type")
 }
 
 // MapKey is used to index maps, where the Go type of the MapKey must match