diff --git a/src/standalone/Soil/Biogeochemistry/co2_parameterizations.jl b/src/standalone/Soil/Biogeochemistry/co2_parameterizations.jl
index cf4db435d3..a9caa31568 100644
--- a/src/standalone/Soil/Biogeochemistry/co2_parameterizations.jl
+++ b/src/standalone/Soil/Biogeochemistry/co2_parameterizations.jl
@@ -25,7 +25,7 @@ function microbe_source(
     Vmax = α_sx * exp(-Ea_sx / (R * T_soil)) # Maximum potential rate of respiration
     Sx = p_sx * Csom * D_liq * θ_l^3 # All soluble substrate, kgC m⁻³
     MM_sx = Sx / (kM_sx + Sx) # Availability of substrate factor, 0-1
-    O2 = D_oa * O2_a * ((ν - θ_l)^(FT(4 / 3))) # Oxygen concentration
+    O2 = D_oa * O2_a * (max((ν - θ_l), 0)^(FT(4 / 3))) # Oxygen concentration
     MM_o2 = O2 / (kM_o2 + O2) # Oxygen limitation factor, 0-1
     R_sm = Vmax * MM_sx * MM_o2 # Respiration, kg C m⁻³ s⁻¹
     return R_sm
@@ -82,7 +82,7 @@ function co2_diffusivity(
     T_ref = FT(LP.T_0(earth_param_set))
     P_ref = FT(LP.P_ref(earth_param_set))
     θ_a = volumetric_air_content(θ_w, ν)
-    D0 = D_ref * (T_soil / T_ref)^FT(1.75) * (P_ref / P_sfc)
+    D0 = D_ref * max((T_soil / T_ref), 0)^FT(1.75) * (P_ref / P_sfc)
     D =
         D0 *
         (FT(2)θ_a100^FT(3) + FT(0.04)θ_a100) *