diff --git a/stackit/internal/services/alb/applicationloadbalancer/resource.go b/stackit/internal/services/alb/applicationloadbalancer/resource.go
index c65da6e28..d86250ebd 100644
--- a/stackit/internal/services/alb/applicationloadbalancer/resource.go
+++ b/stackit/internal/services/alb/applicationloadbalancer/resource.go
@@ -41,6 +41,11 @@ import (
 	"github.com/stackitcloud/terraform-provider-stackit/stackit/internal/validate"
 )
 
+// healthCheckDurationRegex accepts only durations in the form the API returns them: whole seconds
+// ("1s") or exactly three non-zero decimals ("0.100s"), so the value in state matches the config
+// and does not drift. The alternatives are grouped so that both are anchored at both ends.
+var healthCheckDurationRegex = regexp.MustCompile(`^(?:[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s)$`)
+
 // Ensure the implementation satisfies the expected interfaces.
 var (
 	_ resource.Resource                = &applicationLoadBalancerResource{}
@@ -984,7 +989,7 @@ The example below creates the supporting infrastructure using the STACKIT Terraf
 									Required:    true,
 									Validators: []validator.String{
 										stringvalidator.RegexMatches(
-											regexp.MustCompile(`^[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s$`),
+											healthCheckDurationRegex,
 											"The duration must be between 0s and 999.999s (e.g.: 1s or 0.100s or 12.345s)",
 										),
 									},
@@ -994,7 +999,7 @@ The example below creates the supporting infrastructure using the STACKIT Terraf
 									Required:    true,
 									Validators: []validator.String{
 										stringvalidator.RegexMatches(
-											regexp.MustCompile(`^[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s$`),
+											healthCheckDurationRegex,
 											"The duration must be between 0s and 999.999s (e.g.: 1s or 0.100s or 12.345s)",
 										),
 									},
@@ -1004,7 +1009,7 @@ The example below creates the supporting infrastructure using the STACKIT Terraf
 									Required:    true,
 									Validators: []validator.String{
 										stringvalidator.RegexMatches(
-											regexp.MustCompile(`^[0-9]{1,3}s|[0-9]{1,3}\.(?:[0-9]{2}[1-9]|[0-9][1-9][0-9]|[1-9][0-9]{2})s$`),
+											healthCheckDurationRegex,
 											"The duration must be between 0s and 999.999s (e.g.: 1s or 0.100s or 12.345s)",
 										),
 									},
diff --git a/stackit/internal/services/alb/applicationloadbalancer/resource_test.go b/stackit/internal/services/alb/applicationloadbalancer/resource_test.go
index 32d1013fa..922e37530 100644
--- a/stackit/internal/services/alb/applicationloadbalancer/resource_test.go
+++ b/stackit/internal/services/alb/applicationloadbalancer/resource_test.go
@@ -1679,3 +1679,40 @@ func Test_toPathPayload(t *testing.T) {
 		})
 	}
 }
+
+func TestHealthCheckDurationRegex(t *testing.T) {
+	tests := []struct {
+		value string
+		valid bool
+	}{
+		{"0s", true},
+		{"1s", true},
+		{"999s", true},
+		{"0.100s", true},
+		{"1.500s", true},
+		{"12.345s", true},
+		{"999.999s", true},
+		// Returned by the API as "0.100s", "1s" and "0s", which would drift.
+		{"0.1s", false},
+		{"1.000s", false},
+		{"0.000s", false},
+		{"", false},
+		{"s", false},
+		{"1000s", false},
+		{"1.0000s", false},
+		{"1.s", false},
+		{"-1s", false},
+		{"1", false},
+		{"1ms", false},
+		{"5sGARBAGE", false},
+		{"GARBAGE1.500s", false},
+		{"5s1.500s", false},
+	}
+	for _, tt := range tests {
+		t.Run(tt.value, func(t *testing.T) {
+			if got := healthCheckDurationRegex.MatchString(tt.value); got != tt.valid {
+				t.Errorf("healthCheckDurationRegex.MatchString(%q) = %v, want %v", tt.value, got, tt.valid)
+			}
+		})
+	}
+}