diff --git a/damus.xcodeproj/project.pbxproj b/damus.xcodeproj/project.pbxproj
index adfb6c9f..9b096ad4 100644
--- a/damus.xcodeproj/project.pbxproj
+++ b/damus.xcodeproj/project.pbxproj
@@ -5034,6 +5034,8 @@
 				GCC_OPTIMIZATION_LEVEL = 0;
 				GCC_PREPROCESSOR_DEFINITIONS = (
 					"DEBUG=1",
+					"MDB_SHORT_SEMNAMES=1",
+					"MDB_SEM_NAME_PREFIX=\"group.com.damus\"",
 					"$(inherited)",
 				);
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
@@ -5097,7 +5099,10 @@
 				ENABLE_USER_SCRIPT_SANDBOXING = NO;
 				GCC_C_LANGUAGE_STANDARD = gnu11;
 				GCC_NO_COMMON_BLOCKS = YES;
-				"GCC_PREPROCESSOR_DEFINITIONS[arch=*]" = "";
+				GCC_PREPROCESSOR_DEFINITIONS = (
+					"MDB_SHORT_SEMNAMES=1",
+					"MDB_SEM_NAME_PREFIX=\"group.com.damus\"",
+				);
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
 				GCC_WARN_UNDECLARED_SELECTOR = YES;
diff --git a/nostrdb/mdb.c b/nostrdb/mdb.c
index deb67796..c9614a30 100644
--- a/nostrdb/mdb.c
+++ b/nostrdb/mdb.c
@@ -4893,8 +4893,17 @@ mdb_env_setup_locks(MDB_env *env, MDB_name *fname, int mode, int *excl)
 #ifdef MDB_SHORT_SEMNAMES
 		encbuf[9] = '\0';	/* drop name from 15 chars to 14 chars */
 #endif
-		sprintf(env->me_txns->mti_rmname, "/MDBr%s", encbuf);
-		sprintf(env->me_txns->mti_wmname, "/MDBw%s", encbuf);
+
+#define DEF_STR(x) #x
+#define DEF_TO_STRING(x) DEF_STR(x)
+        sprintf(env->me_txns->mti_rmname, DEF_TO_STRING(MDB_SEM_NAME_PREFIX) "/MDBr%s", encbuf);
+        sprintf(env->me_txns->mti_wmname, DEF_TO_STRING(MDB_SEM_NAME_PREFIX) "/MDBw%s", encbuf);
+#undef DEF_STR
+#undef DEF_TO_STRING
+
+		printf("mdb_env_setup_locks: using semnames '%s' (%d), '%s' (%d)\n",
+		       env->me_txns->mti_rmname, strlen(env->me_txns->mti_rmname),
+		       env->me_txns->mti_wmname, strlen(env->me_txns->mti_wmname));
 		/* Clean up after a previous run, if needed:  Try to
 		 * remove both semaphores before doing anything else.
 		 */