diff --git a/src/charon/config/proposal.c b/src/charon/config/proposal.c
index 877b0f40a..e2dfcca4f 100644
--- a/src/charon/config/proposal.c
+++ b/src/charon/config/proposal.c
@@ -645,7 +645,7 @@ static int print_alg(private_proposal_t *this, char **dst, size_t *len,
 		}
 		if (size)
 		{
-			written += print_in_hook(*dst, *len, "-%d", size);
+			written += print_in_hook(*dst, *len, "_%u", size);
 		}
 	}
 	enumerator->destroy(enumerator);
diff --git a/src/charon/plugins/stroke/stroke_list.c b/src/charon/plugins/stroke/stroke_list.c
index d88c3c642..e45b3a936 100644
--- a/src/charon/plugins/stroke/stroke_list.c
+++ b/src/charon/plugins/stroke/stroke_list.c
@@ -193,7 +193,7 @@ static void log_child_sa(FILE *out, child_sa_t *child_sa, bool all)
 					fprintf(out, "%N", encryption_algorithm_names, encr_alg);
 					if (encr_size)
 					{
-						fprintf(out, "-%d", encr_size);
+						fprintf(out, "_%u", encr_size);
 					}
 				}
 				if (int_alg != AUTH_UNDEFINED)
@@ -201,7 +201,7 @@ static void log_child_sa(FILE *out, child_sa_t *child_sa, bool all)
 					fprintf(out, "/%N", integrity_algorithm_names, int_alg);
 					if (int_size)
 					{
-						fprintf(out, "-%d", int_size);
+						fprintf(out, "_%u", int_size);
 					}
 				}
 			}