diff --git a/src/amd_rapl.h b/src/amd_rapl.h
index e58cc16498f4b7553f9a7ebf6b6f40e8cd4ee288..5c555b2a12b2d18173d6f4a775081f4930369dc5 100644
--- a/src/amd_rapl.h
+++ b/src/amd_rapl.h
@@ -37,6 +37,6 @@ Optparse amd_rapl_opt[1] = {
         .shortname = 'r',
         .argtype = OPTPARSE_NONE,
         .usage_arg = NULL,
-        .usage_msg = "AMD RAPL",
+        .usage_msg = "AMD RAPL (micro-joules)",
     },
 };
diff --git a/src/rapl.h b/src/rapl.h
index 7720f071a4be6b98dad5cb72d537bd69a430799d..25b75217773538c2abed25efff7a9caca3ed3bf1 100644
--- a/src/rapl.h
+++ b/src/rapl.h
@@ -37,7 +37,7 @@ Optparse rapl_opt[1] = {
         .shortname = 'r',
         .argtype = OPTPARSE_NONE,
         .usage_arg = NULL,
-        .usage_msg = "INTEL RAPL",
+        .usage_msg = "INTEL RAPL (micro-joules)",
     },
 };