diff --git a/bindings/c/CMakeLists.txt b/bindings/c/CMakeLists.txt
index f4e5a762ac..cf3a4f1a3a 100644
--- a/bindings/c/CMakeLists.txt
+++ b/bindings/c/CMakeLists.txt
@@ -111,6 +111,12 @@ if(NOT WIN32)
   set_property(TARGET mako PROPERTY SKIP_BUILD_RPATH TRUE)
   target_link_libraries(mako PRIVATE fdb_c)
 
+  # Make sure that fdb_c.h is compatible with c90
+  add_executable(fdb_c90_test test/fdb_c90_test.c)
+  set_property(TARGET fdb_c90_test PROPERTY C_STANDARD 90)
+  target_compile_options(fdb_c90_test PRIVATE -Wall -Wextra -Wpedantic -Werror)
+  target_link_libraries(fdb_c90_test PRIVATE fdb_c)
+
   add_fdbclient_test(
     NAME fdb_c_setup_tests
     COMMAND $<TARGET_FILE:fdb_c_setup_tests>)
diff --git a/bindings/c/foundationdb/fdb_c.h b/bindings/c/foundationdb/fdb_c.h
index 1723a4c6ec..5fa7e4d459 100644
--- a/bindings/c/foundationdb/fdb_c.h
+++ b/bindings/c/foundationdb/fdb_c.h
@@ -45,12 +45,17 @@
 #define WARN_UNUSED_RESULT
 #endif
 
-// With default settings, gcc will not warn about unprototyped functions being called, so it
-// is easy to erroneously call a function which is not available at FDB_API_VERSION and then
-// get an error only at runtime.  These macros ensure a compile error in such cases, and
-// attempt to make the compile error slightly informative.
-#define This_FoundationDB_API_function_is_removed_at_this_FDB_API_VERSION() [=====]
-#define FDB_REMOVED_FUNCTION This_FoundationDB_API_function_is_removed_at_this_FDB_API_VERSION(0)
+/*
+ * With default settings, gcc will not warn about unprototyped functions being
+ * called, so it is easy to erroneously call a function which is not available
+ * at FDB_API_VERSION and then get an error only at runtime.  These macros
+ * ensure a compile error in such cases, and attempt to make the compile error
+ * slightly informative.
+ */
+#define This_FoundationDB_API_function_is_removed_at_this_FDB_API_VERSION()    \
+  [== == = ]
+#define FDB_REMOVED_FUNCTION                                                   \
+  This_FoundationDB_API_function_is_removed_at_this_FDB_API_VERSION(0)
 
 #include <stdint.h>
 
@@ -248,12 +253,15 @@ extern "C" {
     fdb_transaction_get_committed_version( FDBTransaction* tr,
                                            int64_t* out_version );
 
-    // This function intentionally returns an FDBFuture instead of an integer directly,
-    // so that calling this API can see the effect of previous mutations on the transaction.
-    // Specifically, mutations are applied asynchronously by the main thread. In order to
-    // see them, this call has to be serviced by the main thread too.
-    DLLEXPORT WARN_UNUSED_RESULT FDBFuture*
-    fdb_transaction_get_approximate_size(FDBTransaction* tr);
+    /*
+     * This function intentionally returns an FDBFuture instead of an integer
+     * directly, so that calling this API can see the effect of previous
+     * mutations on the transaction. Specifically, mutations are applied
+     * asynchronously by the main thread. In order to see them, this call has to
+     * be serviced by the main thread too.
+     */
+    DLLEXPORT WARN_UNUSED_RESULT FDBFuture *
+    fdb_transaction_get_approximate_size(FDBTransaction *tr);
 
     DLLEXPORT WARN_UNUSED_RESULT FDBFuture*
     fdb_get_server_protocol(const char* clusterFilePath);
@@ -305,7 +313,7 @@ extern "C" {
     typedef struct FDB_cluster FDBCluster;
 
     typedef enum {
-        // This option is only a placeholder for C compatibility and should not be used
+        /* This option is only a placeholder for C compatibility and should not be used */
         FDB_CLUSTER_OPTION_DUMMY_DO_NOT_USE=-1
     } FDBClusterOption;
 #endif
diff --git a/bindings/c/test/fdb_c90_test.c b/bindings/c/test/fdb_c90_test.c
new file mode 100644
index 0000000000..1569d98250
--- /dev/null
+++ b/bindings/c/test/fdb_c90_test.c
@@ -0,0 +1,9 @@
+#define FDB_API_VERSION 700
+#include <foundationdb/fdb_c.h>
+
+int main(int argc, char* argv[]) {
+	(void)argc;
+	(void)argv;
+	fdb_select_api_version(700);
+	return 0;
+}
diff --git a/fdbclient/vexillographer/c.cs b/fdbclient/vexillographer/c.cs
index ee718495a5..2ea6675dff 100644
--- a/fdbclient/vexillographer/c.cs
+++ b/fdbclient/vexillographer/c.cs
@@ -52,8 +52,8 @@ namespace vexillographer
         {
             string parameterComment = "";
             if (o.scope.ToString().EndsWith("Option"))
-                parameterComment = String.Format("{0}// {1}\n", indent, "Parameter: " + o.getParameterComment());
-            return String.Format("{0}// {2}\n{5}{0}{1}{3}={4}", indent, prefix, o.comment, o.name.ToUpper(), o.code, parameterComment);
+                parameterComment = String.Format("{0}/* {1} */\n", indent, "Parameter: " + o.getParameterComment());
+            return String.Format("{0}/* {2} */\n{5}{0}{1}{3}={4}", indent, prefix, o.comment, o.name.ToUpper(), o.code, parameterComment);
         }
 
         private static void writeCEnum(TextWriter outFile, Scope scope, IEnumerable<Option> options)