diff --git a/objectivec/GPBCodedInputStream.m b/objectivec/GPBCodedInputStream.m
index fd87783..dd05ddb 100644
--- a/objectivec/GPBCodedInputStream.m
+++ b/objectivec/GPBCodedInputStream.m
@@ -36,17 +36,53 @@
 #import "GPBUtilities_PackagePrivate.h"
 #import "GPBWireFormat.h"
 
-static const NSUInteger kDefaultRecursionLimit = 64;
+NSString *const GPBCodedInputStreamException =
+    GPBNSStringifySymbol(GPBCodedInputStreamException);
+
+NSString *const GPBCodedInputStreamUnderlyingErrorKey =
+    GPBNSStringifySymbol(GPBCodedInputStreamUnderlyingErrorKey);
+
+NSString *const GPBCodedInputStreamErrorDomain =
+    GPBNSStringifySymbol(GPBCodedInputStreamErrorDomain);
+
+// Matching:
+// https://github.com/google/protobuf/blob/master/java/core/src/main/java/com/google/protobuf/CodedInputStream.java#L62
+//  private static final int DEFAULT_RECURSION_LIMIT = 100;
+// https://github.com/google/protobuf/blob/master/src/google/protobuf/io/coded_stream.cc#L86
+//  int CodedInputStream::default_recursion_limit_ = 100;
+static const NSUInteger kDefaultRecursionLimit = 100;
+
+static void RaiseException(NSInteger code, NSString *reason) {
+  NSDictionary *errorInfo = nil;
+  if ([reason length]) {
+    errorInfo = @{ GPBErrorReasonKey: reason };
+  }
+  NSError *error = [NSError errorWithDomain:GPBCodedInputStreamErrorDomain
+                                       code:code
+                                   userInfo:errorInfo];
+
+  NSDictionary *exceptionInfo =
+      @{ GPBCodedInputStreamUnderlyingErrorKey: error };
+  [[NSException exceptionWithName:GPBCodedInputStreamException
+                           reason:reason
+                         userInfo:exceptionInfo] raise];
+}
+
+static void CheckRecursionLimit(GPBCodedInputStreamState *state) {
+  if (state->recursionDepth >= kDefaultRecursionLimit) {
+    RaiseException(GPBCodedInputStreamErrorRecursionDepthExceeded, nil);
+  }
+}
 
 static void CheckSize(GPBCodedInputStreamState *state, size_t size) {
   size_t newSize = state->bufferPos + size;
   if (newSize > state->bufferSize) {
-    [NSException raise:NSParseErrorException format:@""];
+    RaiseException(GPBCodedInputStreamErrorInvalidSize, nil);
   }
   if (newSize > state->currentLimit) {
     // Fast forward to end of currentLimit;
     state->bufferPos = state->currentLimit;
-    [NSException raise:NSParseErrorException format:@""];
+    RaiseException(GPBCodedInputStreamErrorSubsectionLimitReached, nil);
   }
 }
 
@@ -69,56 +105,25 @@
   return value;
 }
 
-static int32_t ReadRawVarint32(GPBCodedInputStreamState *state) {
-  int8_t tmp = ReadRawByte(state);
-  if (tmp >= 0) {
-    return tmp;
-  }
-  int32_t result = tmp & 0x7f;
-  if ((tmp = ReadRawByte(state)) >= 0) {
-    result |= tmp << 7;
-  } else {
-    result |= (tmp & 0x7f) << 7;
-    if ((tmp = ReadRawByte(state)) >= 0) {
-      result |= tmp << 14;
-    } else {
-      result |= (tmp & 0x7f) << 14;
-      if ((tmp = ReadRawByte(state)) >= 0) {
-        result |= tmp << 21;
-      } else {
-        result |= (tmp & 0x7f) << 21;
-        result |= (tmp = ReadRawByte(state)) << 28;
-        if (tmp < 0) {
-          // Discard upper 32 bits.
-          for (int i = 0; i < 5; i++) {
-            if (ReadRawByte(state) >= 0) {
-              return result;
-            }
-          }
-          [NSException raise:NSParseErrorException
-                      format:@"Unable to read varint32"];
-        }
-      }
-    }
-  }
-  return result;
-}
-
 static int64_t ReadRawVarint64(GPBCodedInputStreamState *state) {
   int32_t shift = 0;
   int64_t result = 0;
   while (shift < 64) {
     int8_t b = ReadRawByte(state);
-    result |= (int64_t)(b & 0x7F) << shift;
+    result |= (int64_t)((uint64_t)(b & 0x7F) << shift);
     if ((b & 0x80) == 0) {
       return result;
     }
     shift += 7;
   }
-  [NSException raise:NSParseErrorException format:@"Unable to read varint64"];
+  RaiseException(GPBCodedInputStreamErrorInvalidVarInt, @"Invalid VarInt64");
   return 0;
 }
 
+static int32_t ReadRawVarint32(GPBCodedInputStreamState *state) {
+  return (int32_t)ReadRawVarint64(state);
+}
+
 static void SkipRawData(GPBCodedInputStreamState *state, size_t size) {
   CheckSize(state, size);
   state->bufferPos += size;
@@ -200,10 +205,15 @@
   }
 
   state->lastTag = ReadRawVarint32(state);
-  if (state->lastTag == 0) {
-    // If we actually read zero, that's not a valid tag.
-    [NSException raise:NSParseErrorException
-                format:@"Invalid last tag %d", state->lastTag];
+  // Tags have to include a valid wireformat.
+  if (!GPBWireFormatIsValidTag(state->lastTag)) {
+    RaiseException(GPBCodedInputStreamErrorInvalidTag,
+                   @"Invalid wireformat in tag.");
+  }
+  // Zero is not a valid field number.
+  if (GPBWireFormatGetTagFieldNumber(state->lastTag) == 0) {
+    RaiseException(GPBCodedInputStreamErrorInvalidTag,
+                   @"A zero field number on the wire is invalid.");
   }
   return state->lastTag;
 }
@@ -219,15 +229,15 @@
     result = [[NSString alloc] initWithBytes:&state->bytes[state->bufferPos]
                                       length:size
                                     encoding:NSUTF8StringEncoding];
+    state->bufferPos += size;
     if (!result) {
-      result = @"";
 #ifdef DEBUG
       // https://developers.google.com/protocol-buffers/docs/proto#scalar
-      NSLog(@"UTF8 failure, is some field type 'string' when it should be "
+      NSLog(@"UTF-8 failure, is some field type 'string' when it should be "
             @"'bytes'?");
 #endif
+      RaiseException(GPBCodedInputStreamErrorInvalidUTF8, nil);
     }
-    state->bufferPos += size;
   }
   return result;
 }
@@ -261,8 +271,7 @@
   byteLimit += state->bufferPos;
   size_t oldLimit = state->currentLimit;
   if (byteLimit > oldLimit) {
-    [NSException raise:NSInvalidArgumentException
-                format:@"byteLimit > oldLimit: %tu > %tu", byteLimit, oldLimit];
+    RaiseException(GPBCodedInputStreamErrorInvalidSubsectionLimit, nil);
   }
   state->currentLimit = byteLimit;
   return oldLimit;
@@ -285,8 +294,7 @@
 void GPBCodedInputStreamCheckLastTagWas(GPBCodedInputStreamState *state,
                                         int32_t value) {
   if (state->lastTag != value) {
-    [NSException raise:NSParseErrorException
-                format:@"Last tag: %d should be %d", state->lastTag, value];
+    RaiseException(GPBCodedInputStreamErrorInvalidTag, @"Unexpected tag read");
   }
 }
 
@@ -315,6 +323,12 @@
   [super dealloc];
 }
 
+// Direct access is use for speed, to avoid even internally declaring things
+// read/write, etc. The warning is enabled in the project to ensure code calling
+// protos can turn on -Wdirect-ivar-access without issues.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdirect-ivar-access"
+
 - (int32_t)readTag {
   return GPBCodedInputStreamReadTag(&state_);
 }
@@ -324,6 +338,7 @@
 }
 
 - (BOOL)skipField:(int32_t)tag {
+  NSAssert(GPBWireFormatIsValidTag(tag), @"Invalid tag");
   switch (GPBWireFormatGetTagWireType(tag)) {
     case GPBWireFormatVarint:
       GPBCodedInputStreamReadInt32(&state_);
@@ -346,8 +361,6 @@
       SkipRawData(&state_, sizeof(int32_t));
       return YES;
   }
-  [NSException raise:NSParseErrorException format:@"Invalid tag %d", tag];
-  return NO;
 }
 
 - (void)skipMessage {
@@ -359,6 +372,22 @@
   }
 }
 
+- (BOOL)isAtEnd {
+  return GPBCodedInputStreamIsAtEnd(&state_);
+}
+
+- (size_t)position {
+  return state_.bufferPos;
+}
+
+- (size_t)pushLimit:(size_t)byteLimit {
+  return GPBCodedInputStreamPushLimit(&state_, byteLimit);
+}
+
+- (void)popLimit:(size_t)oldLimit {
+  GPBCodedInputStreamPopLimit(&state_, oldLimit);
+}
+
 - (double)readDouble {
   return GPBCodedInputStreamReadDouble(&state_);
 }
@@ -398,11 +427,7 @@
 - (void)readGroup:(int32_t)fieldNumber
               message:(GPBMessage *)message
     extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
-  if (state_.recursionDepth >= kDefaultRecursionLimit) {
-    [NSException raise:NSParseErrorException
-                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
-                       kDefaultRecursionLimit];
-  }
+  CheckRecursionLimit(&state_);
   ++state_.recursionDepth;
   [message mergeFromCodedInputStream:self extensionRegistry:extensionRegistry];
   GPBCodedInputStreamCheckLastTagWas(
@@ -412,11 +437,7 @@
 
 - (void)readUnknownGroup:(int32_t)fieldNumber
                  message:(GPBUnknownFieldSet *)message {
-  if (state_.recursionDepth >= kDefaultRecursionLimit) {
-    [NSException raise:NSParseErrorException
-                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
-                       kDefaultRecursionLimit];
-  }
+  CheckRecursionLimit(&state_);
   ++state_.recursionDepth;
   [message mergeFromCodedInputStream:self];
   GPBCodedInputStreamCheckLastTagWas(
@@ -426,12 +447,8 @@
 
 - (void)readMessage:(GPBMessage *)message
     extensionRegistry:(GPBExtensionRegistry *)extensionRegistry {
+  CheckRecursionLimit(&state_);
   int32_t length = ReadRawVarint32(&state_);
-  if (state_.recursionDepth >= kDefaultRecursionLimit) {
-    [NSException raise:NSParseErrorException
-                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
-                       kDefaultRecursionLimit];
-  }
   size_t oldLimit = GPBCodedInputStreamPushLimit(&state_, length);
   ++state_.recursionDepth;
   [message mergeFromCodedInputStream:self extensionRegistry:extensionRegistry];
@@ -444,12 +461,8 @@
     extensionRegistry:(GPBExtensionRegistry *)extensionRegistry
                 field:(GPBFieldDescriptor *)field
         parentMessage:(GPBMessage *)parentMessage {
+  CheckRecursionLimit(&state_);
   int32_t length = ReadRawVarint32(&state_);
-  if (state_.recursionDepth >= kDefaultRecursionLimit) {
-    [NSException raise:NSParseErrorException
-                format:@"recursionDepth(%tu) >= %tu", state_.recursionDepth,
-                       kDefaultRecursionLimit];
-  }
   size_t oldLimit = GPBCodedInputStreamPushLimit(&state_, length);
   ++state_.recursionDepth;
   GPBDictionaryReadEntry(mapDictionary, self, extensionRegistry, field,
@@ -487,4 +500,6 @@
   return GPBCodedInputStreamReadSInt64(&state_);
 }
 
+#pragma clang diagnostic pop
+
 @end