diff --git a/Makefile.am b/Makefile.am
index 85b317f..8b822ab 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -178,6 +178,19 @@ t/test-full.pb.cc t/test-full.pb.h: @PROTOC@ $(top_srcdir)/t/test-full.proto
 t/generated-code2/test-full-cxx-output.inc: t/generated-code2/cxx-generate-packed-data$(EXEEXT)
 	$(AM_V_GEN)$(top_builddir)/t/generated-code2/cxx-generate-packed-data$(EXEEXT) > $(top_builddir)/t/generated-code2/test-full-cxx-output.inc
 
+BUILT_SOURCES += \
+	t/test.pb-c.c t/test.pb-c.h \
+	t/test-full.pb-c.c t/test-full.pb-c.h \
+	t/test-optimized.pb-c.c t/test-optimized.pb-c.h \
+	t/test-full.pb.cc t/test-full.pb.h \
+	t/generated-code2/test-full-cxx-output.inc
+
+t_version_version_SOURCES = \
+	t/version/version.c
+t_version_version_LDADD = \
+	protobuf-c/libprotobuf-c.la
+
+# Issue #220
 check_PROGRAMS += \
 	t/issue220/issue220
 TESTS += \
@@ -194,17 +207,23 @@ BUILT_SOURCES += \
 EXTRA_DIST += \
 	t/issue220/issue220.proto
 
-BUILT_SOURCES += \
-	t/test.pb-c.c t/test.pb-c.h \
-	t/test-full.pb-c.c t/test-full.pb-c.h \
-	t/test-optimized.pb-c.c t/test-optimized.pb-c.h \
-	t/test-full.pb.cc t/test-full.pb.h \
-	t/generated-code2/test-full-cxx-output.inc
-
-t_version_version_SOURCES = \
-	t/version/version.c
-t_version_version_LDADD = \
+# Issue #251
+check_PROGRAMS += \
+	t/issue251/issue251
+TESTS += \
+	t/issue251/issue251
+t_issue251_issue251_SOURCES = \
+	t/issue251/issue251.c \
+	t/issue251/issue251.pb-c.c
+t_issue251_issue251_LDADD = \
 	protobuf-c/libprotobuf-c.la
+t/issue251/issue251.pb-c.c t/issue251/issue251.pb-c.h: $(top_builddir)/protoc-c/protoc-gen-c$(EXEEXT) $(top_srcdir)/t/issue251/issue251.proto
+	$(AM_V_GEN)@PROTOC@ --plugin=$(top_builddir)/protoc-c/protoc-gen-c$(EXEEXT) -I$(top_srcdir) --c_out=$(top_builddir) $(top_srcdir)/t/issue251/issue251.proto
+BUILT_SOURCES += \
+	t/issue251/issue251.pb-c.c t/issue251/issue251.pb-c.h
+EXTRA_DIST += \
+	t/issue251/issue251.proto
+
 endif # CROSS_COMPILING
 
 endif # BUILD_COMPILER
diff --git a/protoc-c/c_message.cc b/protoc-c/c_message.cc
index 671b708..4c27cd1 100755
--- a/protoc-c/c_message.cc
+++ b/protoc-c/c_message.cc
@@ -148,9 +148,10 @@ GenerateStructDefinition(io::Printer* printer) {
   }
 
   // Generate the case enums for unions
-  vars["opt_comma"] = ",";
   for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
     const OneofDescriptor *oneof = descriptor_->oneof_decl(i);
+    vars["opt_comma"] = ",";
+
     vars["oneofname"] = FullNameToUpper(oneof->name());
     vars["foneofname"] = FullNameToC(oneof->full_name());
 
@@ -167,7 +168,7 @@ GenerateStructDefinition(io::Printer* printer) {
       }
       printer->Print(vars, "$ucclassname$__$oneofname$_$fieldname$ = $fieldnum$$opt_comma$\n");
     }
-    printer->Print(vars, "  PROTOBUF_C__FORCE_ENUM_TO_BE_INT_SIZE($ucclassname$)\n");
+    printer->Print(vars, "  PROTOBUF_C__FORCE_ENUM_TO_BE_INT_SIZE($ucclassname$__$oneofname$)\n");
     printer->Outdent();
     printer->Print(vars, "} $foneofname$Case;\n\n");
   }
diff --git a/t/issue220/issue220.c b/t/issue220/issue220.c
index 803eb04..530f755 100644
--- a/t/issue220/issue220.c
+++ b/t/issue220/issue220.c
@@ -8,6 +8,6 @@ int main(void)
 {
 	assert(_MESSAGE_TYPE1__FLAG_IS_INT_SIZE == INT_MAX);
 	assert(_MESSAGE_TYPE2__ANOTHER_FLAG_IS_INT_SIZE == INT_MAX);
-	assert(_TOP_LEVEL_IS_INT_SIZE == INT_MAX);
+	assert(_TOP_LEVEL__SUBMESSAGES_IS_INT_SIZE == INT_MAX);
 	return EXIT_SUCCESS;
 }
diff --git a/t/issue251/.gitignore b/t/issue251/.gitignore
new file mode 100644
index 0000000..9ac717d
--- /dev/null
+++ b/t/issue251/.gitignore
@@ -0,0 +1 @@
+issue251
diff --git a/t/issue251/issue251.c b/t/issue251/issue251.c
new file mode 100644
index 0000000..928da56
--- /dev/null
+++ b/t/issue251/issue251.c
@@ -0,0 +1,12 @@
+#include <stdlib.h>
+
+#include "t/issue251/issue251.pb-c.h"
+
+int main(void)
+{
+	/*
+	 * The problem in #251 caused invalid code to be generated in the
+	 * .pb-c.h file, so there's nothing for us to do here.
+	 */
+	return EXIT_SUCCESS;
+}
diff --git a/t/issue251/issue251.proto b/t/issue251/issue251.proto
new file mode 100644
index 0000000..a451894
--- /dev/null
+++ b/t/issue251/issue251.proto
@@ -0,0 +1,11 @@
+message two_oneofs {
+    oneof first_oneof {
+        bool a = 10;
+        bool b = 11;
+    }
+
+    oneof second_oneof {
+        bool c = 20;
+        bool d = 21;
+    }
+}